This study is a multicenter, randomized, double-blind, placebo- and active-controlled Phase III clinical trial sponsored by Nanjing Shunxin Pharmaceutical Co., Ltd., a subsidiary of Chiatai Tianqing Pharmaceutical Group. The study aims to evaluate the efficacy and safety of once-daily oral TQH3906 capsules (24 mg) in adult participants with moderate to severe plaque psoriasis. TQH3906 is a highly selective TYK2 allosteric inhibitor targeting the JH2 domain, which blocks the IL-23 and Type I interferon inflammatory pathways. Approximately 400 eligible participants aged 18-75 years will be enrolled. Participants will be stratified based on prior biologic use and randomized in a 2:2:1 ratio to the TQH3906 group, the deucravacitinib active control group, or the placebo group. The trial includes a screening period, a 16-week double-blind controlled treatment phase, a 36-week open-label extension phase (during which all participants will receive TQH3906), and a 4-week safety follow-up after the last dose. The co-primary endpoints are the proportion of participants achieving sPGA 0/1 and PASI 90 response at Week 16. Secondary endpoints include improvements in scalp, nail, and palmoplantar psoriasis, Dermatology Life Quality Index (DLQI), long-term safety, and steady-state pharmacokinetic parameters. This study will collect comprehensive efficacy and safety data over 52 weeks to support the New Drug Application (NDA) for TQH3906 for the treatment of plaque psoriasis.