This study is a marketing-oriented clinical trial of TQH3906 Capsules. A total of 156 participants are planned to be enrolled, aiming to evaluate the dose-effect relationship of TQH3906 versus placebo in the treatment of active Psoriatic Arthritis (PsA) at Week 12, with the proportion of participants achieving an American College of Rheumatology 20% (ACR20) Improvement Criteria (ACR20) response at Week 12 as the primary endpoint.

Inclusion Criteria:

• Sign a written Informed Consent Form, which must meet the following requirements

  • Be willing to participate in the study and able to sign the informed consent form;
  • Be willing and able to complete all study-specific procedures and visits;

• PsA trial participant disease characteristics

  • Aged 18 to 70 years（inclusive）;
  • BMI ≥ 18 kg/m² at screening; diagnosed with PsA for at least 3 months prior to screening, and meeting the Classification Criteria for Psoriatic Arthritis (CASPAR) at screening;
  • Active arthritis at screening and at baseline (Day 1);
  • Has failed or was intolerant to at least one prior therapy;
  • If receiving a conventional synthetic Disease-Modifying Antirheumatic Drug (csDMARD), trial participants must be on only one DMARD, which must have been administered for at least 3 months prior to screening, with a stable dose for at least 28 days prior to the first dose;
  • If using NSAIDs, the dose must have been stable for at least 14 days before the first dose;
  • If using oral corticosteroids, the dose must have been stable for at least 14 days before the first dose;
  • Topical treatments for plaque psoriasis must have remained stable for at least 14 days before the first dose;

• Women of childbearing potential must agree to use effective contraception during the study and for 6 months after the end of the study; men must agree to use effective contraception during the study and for 6 months after the end of the study

Exclusion Criteria:

• Presence of conditions other than PsA:

  • Presence of non-plaque psoriasis (i.e., guttate, inverse, pustular, erythrodermic, or drug-induced psoriasis) at screening or first dose;
  • Presence of any other autoimmune disease, such as rheumatoid arthritis, systemic lupus erythematosus, etc.;
  • Presence of active (i.e., currently symptomatic) fibromyalgia;

• Other Medical Conditions and Medical History:

  • Trial participants who are pregnant or breastfeeding;
  • Evidence of a serious illness/condition or unstable clinical condition, or localized active infection/infectious disease;
  • Any major surgery performed within 30 days prior to the first dose of study treatment, or any planned surgery during the study;
  • Cancer or a history of cancer or lymphoproliferative disease within the past 5 years;
  • New York Heart Association (NYHA) Class III or IV congestive heart failure, or any recent episode of heart failure resulting in NYHA Class III/IV symptoms; or a history of clinically significant ventricular arrhythmia or arrhythmia requiring continuous antiarrhythmic drug therapy;
  • Uncontrolled hypertension at screening or randomization;
  • History of thrombotic disease within 24 weeks prior to screening; viii. History of acute coronary syndrome and/or any major cerebrovascular disease within 24 weeks prior to screening;
  • Current or recent (within 3 months prior to randomization) gastrointestinal disease that may affect absorption of study treatment, including gastrointestinal surgery;
  • Severe blood loss (> 500 mL) or blood transfusion within 4 weeks prior to randomization;
  • Inability to take oral medication;
  • Inability to undergo venipuncture and/or tolerate venous access;
  • History of substance abuse with inability to abstain or presence of a psychiatric disorder;
  • Any other medical, psychiatric, and/or social reason as determined by medical judgment;

• Prior and concomitant medications: If the trial participant has a history of biologic use, the exclusion criteria specified in the protocol will apply;

• Infection-related:

  • Active tuberculosis identified by chest radiography within 6 months prior to screening; trial participants with a negative chest radiography within 3 months prior to screening are eligible if they meet the protocol requirements;
  • Hepatitis C, hepatitis B, or human immunodeficiency virus (HIV) infection; or syphilis infection requiring treatment;

• Abnormal physical examination or laboratory findings;

• Other:

  • History of any major drug allergy; known allergy to any excipient of the investigational product;
  • Inability to comply with the trial protocol;
  • History of substance abuse with inability to abstain or presence of a psychiatric disorder;
  • Participation in another clinical trial and use of another investigational drug (other than for psoriatic arthritis) within 4 weeks prior to the first dose, based on the date of discontinuation from the previous trial;
  • Planned or previous allogeneic bone marrow transplantation or solid organ transplantation;
  • Any condition that, in the investigator's judgment, poses a serious risk to the safety of the trial participant or affects the participant's ability to complete the study.