This is a Phase 1, randomized, double-blind, placebo-controlled, multiple ascending dose study designed to evaluate the safety, tolerability, and pharmacokinetics of IBI3033 in subjects with moderate-to-severe atopic dermatitis (AD). Approximately 16 eligible adult participants will be enrolled and sequentially assigned to one of two dose cohorts. Within each cohort, participants will be randomized in a 3:1 ratio to receive IBI3033 or matching placebo. The study consists of a screening period (up to 4 weeks), a 12-week treatment period, and a 4-week safety follow-up period. The primary objective is to assess safety and tolerability based on the incidence of adverse events and serious adverse events. Secondary objectives include characterization of pharmacokinetics and immunogenicity. Exploratory assessments include pharmacodynamic biomarkers and preliminary efficacy outcomes such as changes in Eczema Area and Severity Index (EASI) and Investigator's Global Assessment (vIGA-AD) scores.

Inclusion Criteria:

1. Ability to understand and sign written informed consent prior to any study procedures and willingness to comply with study requirements throughout the study.

2. Age between 18 and 75 years old (inclusive).

3. Body weight ≥40 kg, with a Body Mass Index (BMI) between 18 and 35 kg/m² (inclusive).

4. Participants of childbearing potential and their partners must agree to strictly follow contraceptive measures specified in the protocol during the study and for 6 months after study completion.

   At the time of screening, meet the diagnostic criteria for atopic dermatitis according to the 2014 American Academy of Dermatology consensus, and have been diagnosed with AD for at least 12 months.

5. At screening and randomization, participants must have an EASI score ≥16, vIGA-AD score ≥3, involved body surface area (BSA) ≥10%, and baseline PP-NRS ≥4.

6. History of inadequate response to topical therapy within the past 12 months, or documented medical reasons making topical therapy unsuitable (e.g., severe adverse reactions or safety concerns).

Exclusion Criteria:

1. Clinically significant diseases that may affect safety or study participation, including but not limited to psychiatric, CNS, cardiovascular, digestive, respiratory, urinary, hematologic, or metabolic disorders.
2. Known history of active tuberculosis or clinically suspected tuberculosis (including but not limited to pulmonary tuberculosis, lymph node tuberculosis, tuberculous pleurisy, etc.); or chest imaging suggestive of suspected tuberculosis; or any other clinical evidence of latent tuberculosis.
3. History of malignant tumors, except for surgically removed or cured localized basal cell carcinoma (BCC) or squamous cell carcinoma (SCC) of the skin.
4. History of severe systemic allergic reactions (e.g., anaphylaxis, laryngeal edema).
5. Fainting at the sight of needles, blood, or inability to tolerate intravenous puncture.
6. Pregnant or breastfeeding women, or female participants who test positive for pregnancy during screening or at randomization.
7. Receipt of other investigational drugs within 3 months or 5 half-lives before randomization (whichever is longer), or current participation in another clinical trial.
8. Had a serious infection (defined as requiring hospitalization or intravenous anti-infective therapy) or trauma within the 3 months prior to randomization, or a history of surgery within 3 months, or an infection requiring oral medication within 1 month, or plans to undergo surgery during the study period.
9. Receipt of any live vaccines (except influenza vaccine) within 1 month before randomization, or planning to receive vaccination during the study.
10. History of parasitic infections within 6 months before screening, or planning to travel to parasite-endemic countries/regions in Africa, South America, and southern parts of Asia (including Southeast Asia, India, Nepal) within 6 months after study completion.