This is a multicenter, randomized, double-blinded，controlled clinical trial. The purpose of the study is to evaluate the efficacy and safety of Sulodexide versus placebo in preventing psoriasis recurrence in patients with plaque psoriasis who have discontinued biologic therapy after achieving clinical cure.

It was planned to include 160 patients with psoriasis vulgaris who met the inclusion criteria for discontinuation of biologics after reaching the standard of treatment and were randomised in a 1:1 ratio to receive oral treatment with sulodexide soft capsules or placebo capsules, respectively.

1. Sulodexide group： Starting after the last injection of secukinumab, oral treatment with sulodexide soft capsule (Alpha Weissmann Pharmaceuticals, Italy, approval number H20140119, specification 250 LSU) was given as 1 tab bid for 120 days or discontinued after judged to be a relapse;
2. Control group: Oral treatment with placebo capsule, 1 tab bid starting after the last injection of secukinumab, discontinued after 120 days of continuous oral administration or judged to be discontinued for relapse.

Inclusion Criteria:

1. Age is 18-65 years old and gender is not limited;
2. Clinical diagnosis consistent with moderate to severe plaque psoriasis;
3. After receiving standardised treatment with strychnicolizumab for 3 months to achieve complete clearing of skin lesions (in accordance with PASI 100 or PGA 0), and then continuing the treatment for 6 months without symptomatic relapse to satisfy the criteria for discontinuation of the drug and discontinuing strychnicolizumab (refer to the recommendations of 'Guidelines for the treatment of psoriasis with biologics in China (2021 edition)');
4. Voluntarily participate in the study and sign the informed consent form before the start of the study.

Exclusion Criteria:

1. Suffering from severe systemic or localised infections within the last 6 months;
2. Those with bleeding tendency or suffering from bleeding disorders;
3. The presence of malignant tumours, or postoperative tumour patients and those at high risk of tumours;
4. Have received or currently require treatment with other anticoagulant drugs such as sulodexide drugs within the last 9 months (e.g. argatroban, bivalirudin, dabigatran etexilate, desirudin, lepirudin, aspirin, etc.);
5. Treatment with other biological agents within the last 9 months;
6. Highly allergic or with a history of severe allergies; allergy to heparin or heparin analogues; or known/suspected allergy to one of the components of the investigational drug;
7. Infection with other diseases such as Human Immunodeficiency Virus (HIV);
8. Serious, progressive, uncontrolled disorders of vital organs and systems (including cardiovascular, hepatic, pulmonary, and renal) and other diseases that, in the opinion of the investigator, are not suitable for participation in the study in combination;
9. Clinically significant abnormal values on screening tests as determined by the investigator;
10. Pregnant women or women of childbearing potential who intend to become pregnant or breastfeeding during the trial period;
11. A positive serum or urine pregnancy test in a female of childbearing potential during the Screening Period;
12. Currently participating in another clinical study or have participated in another clinical study within 3 months;
13. Known presence of alcoholism, drug dependence, or psychiatric disorders
14. Known or suspected to be unable to complete the trial due to poor adherence;
15. Who, in the judgement of the investigator, are unsuitable for participation in this clinical study.