A Multicenter, Randomized, Double-Blind, Placebo-Controlled Phase III Clinical Study to Evaluate the Efficacy and Safety of RSS0393 Ointment in Adult Patients With Plaque Psoriasis.

Inclusion Criteria:

1. Age must be ≥18 years on the day of signing the informed consent form, male or female.
2. Body Mass Index (BMI = weight [kg] / height² [m²]) ≥18.0 kg/m² at screening.
3. A history of plaque psoriasis for ≥6 months.
4. Body Surface Area (BSA) involvement of psoriasis lesions between 2% and 20%, and a Psoriasis Area and Severity Index (PASI) score ≥2, and a Physician's Global Assessment (PGA) score ≥2 at both screening and baseline.

Exclusion Criteria:

1. Presence of any of the following skin abnormalities or conditions:

   The participant is diagnosed with skin diseases or conditions other than plaque psoriasis during the screening period that, in the investigator's opinion, may interfere with the evaluation of study-related endpoints.

2. Use of any of the following medications or participation in clinical studies:

1) Treatment with topical anti-psoriatic medications within 14 days prior to baseline, or systemic anti-psoriatic therapies or phototherapy within 28 days prior to baseline, or biologics for psoriasis within the protocol-specified washout period prior to baseline.

2) Participation in any clinical study (including investigational vaccines) or medical device trial within 3 months prior to baseline or within 5 elimination half-lives of the prior investigational product (whichever is longer).

3.Presence of any significant medical histories or underlying conditions that may affect safety.

4.Any of the following laboratory abnormalities and/or 12-lead ECG findings at screening/baseline:

1. Hemoglobin <100.0 g/L (for males) or <90.0 g/L (for females);
2. White blood cell count <3.0 × 10⁹/L;
3. Neutrophil count <1.5 × 10⁹/L;
4. Platelet count <100 × 10⁹/L;
5. Alanine aminotransferase (ALT) or aspartate aminotransferase (AST) >2.5 × the upper limit of normal (ULN);
6. Total bilirubin (TBIL) >1.5 × ULN;
7. Estimated glomerular filtration rate (eGFR) calculated by the Modification of Diet in Renal Disease (MDRD) study equation <60 mL/min/1.73 m², or serum creatinine outside the normal range, and considered by the investigator as unsuitable for study participation;
8. Positive test for hepatitis B surface antigen (HBsAg), human immunodeficiency virus (HIV) antibody, syphilis antibody, or anti-hepatitis C virus (HCV) antibody; OR a 12-lead ECG showing clinically significant abnormalities that may affect participant safety.

5. General Conditions:

1. Women who are pregnant or breastfeeding.
2. Known hypersensitivity to the investigational product or any of its excipients.
3. History or suspicion of alcohol abuse, drug abuse, or substance abuse, in the investigator's judgment.
4. Administration of a live-attenuated vaccine within 12 weeks prior to randomization, intention to receive a live-attenuated vaccine during the study, or participation in a vaccine clinical trial within 12 weeks prior to randomization.
5. Donation of approximately 500 mL of blood within 8 weeks prior to randomization, or plans to donate blood during the study period.
6. Anticipated use of artificial or natural ultraviolet (UV) light exposure (e.g., phototherapy, tanning beds, extensive sun exposure) on the treatment areas during the study treatment period, which, in the investigator's judgment, could interfere with efficacy evaluations.