The purpose of this study is to assess the efficacy and safety of HSK44459 administered orally for moderate to severe plaque psoriasis in adults.

Patients with moderate to severe plaque psoriasis will be randomized into 3 cohorts (dose level 1, dose level 2 and placebo). Approximately 150 subjects will be enrolled. This study includes an 16-week treatment Period, then a 4-week safety visit period.

Inclusion Criteria:

• Fully understand and voluntarily participate this trial, and sign the informed consent form;
• Age≥18 years, regardless of gender;
• Plaque psoriasis;
• A candidate for systemic therapy;
• Agree to use a highly effective method(s) of from the signing of the informed consent form to 3 months post-treatment.

Exclusion Criteria:

• Can not discontinue the prohibited medications specified in the protocol before the first dose and throughout the entire study period;
• Laboratory abnormalities with clinical significance;
• Forms of psoriasis other than chronic plaque-type;
• Presence of other dermatological or autoimmune diseases;
• Presence of active infection requiring systemic therapy;
• Has undergone or plans to undergo major surgery;
• History of cardiovascular or cerebrovascular diseases;
• History of suicide attempts or major psychiatric disorders;
• History of malignant tumors;
• History of gastrointestinal surgery or diseases that may have impact on the study;
• History of drug abuse, illicit drug use, or alcohol abuse;
• History of severe drug allergies;
• Pregnant or lactating women;
• Subjects with any other factor considered by the investigator to be ineligible for participation in the trial.