To evaluate clinical efficacy and safety of injectable recombinant human LFA3-antibody fusion protein (rhLFA3-IgFP), a multi-center, randomized, double-blind, double-dummy, parallel-controlled clinical trial was performed in 212 cases of moderate to severe psoriasis. Intramuscular injection of rhLFA3-IgFP (15 mg/week) and oral administration of blank dummy methotrexate at the dose of 7.5 mg/week was performed in the patients in the experimental group, and control patients were orally administered with methotrexate at the dose of 7.5 mg/week and intramuscularly injected with the blank dummy rhLFA3-IgFP (15 mg/week). PASI was determined prior to and at 2, 4, 6, 8, 12, 16, 20 weeks after the treatment. The efficacy evaluation was carried out on 192 patients, and no significant differences were found in PASI50, PASI75 & PASI90 between the two groups after twelve weeks' treatment (p>0.05). After discontinuation, PASI scores continued to decrease drastically in the experiment group, whereas they increased in the control group. At 8 weeks after discontinuation, PASI scores were decreased by 62.32% (p<0.05) and 52.67% (p<0.05) in the experimental and control groups, respectively. No serious adverse reactions were observed. In conclusion, the results of our investigation demonstrated that rhLFA3-IgFP was an effective therapy for chronic plaque psoriasis with lasting action and low incidence of adverse reactions.