This is a multiple-center, randomized, double-blind, placebo-controlled Phase IIb study to evaluate the efficacy and safety of AK101, an anti-IL-12/23 p40 antibody, when administered subcutaneously, in subjects with moderate-to-severe plaque psoriasis. The study will consist of 3 periods: up to 4 weeks screening, 12 weeks double-blinded treatment and long-term follow-up period(up to 52 weeks).

Inclusion Criteria:

1. Have had Plaque Psoriasis diagnosed at least 6 months prior to screening.
2. Clinical diagnosis of stable plaque psoriasis with involvement of ≥ 10% body surface area. Psoriasis area and severity index(PASI) ≥12. Physicians Global Assessment score ≥3.
3. Candidate for systemic therapy, defined as having psoriasis inadequately controlled by topical treatment (including topical corticosteroids) and/or phototherapy and/or previous systemic therapy.
4. Women of childbearing potential should not be in pregnancy or lactation, men and women of childbearing potential must agree to use adequate birth control measures during study participation and for 6 months after the last doses of study treatment.
5. Ability to provide written informed consent and to be compliant with the schedule of protocol assessments.
6. Willing and able to comply with scheduled visits, treatment plan, laboratory tests, and other study procedures as specified in the protocol.

Exclusion Criteria:

1. Had nonplaque forms of psoriasis (e.g., Guttate, erythrodermic, or pustular).
2. Had other active skin diseases or skin infections (e.g., Bacterial, fungal or viral infection) that could affect psoriasis evaluation.
3. Had imaging diagnosis of pulmonary infection or fibrosis during the 3 months prior to screening.
4. History or evidence of active or latent tuberculosis at screening.
5. Serious systemic infections or local infections during the 2 months prior to screening.
6. History of cancer, including solid tumors and hematological malignancies (except basal cell and in situ squamous cell carcinomas of the skin that have been excised and resolved).
7. Known allergy or hypersensitivity to any biologic therapy at screening that would pose an unacceptable risk to the subject if participating in this study.
8. Known history of alcohol or drug abuse.
9. History or known presence of recurrent or chronic infection (e.g., hepatitis or C, human immunodeficiency virus [HIV], syphilis, TB).
10. Had received any DMARDs (e.g., Anti-malaria drug, retinoids, interferon, lithium) during 2 weeks prior to screening.
11. Had received any physical therapy (e.g., PUVA, ultra-violet therapy, tanning beds) during 2 weeks prior to screening.
12. Had received any systemic psoriasis therapy (e.g., Glucocorticoid, retinoids, ciclosporin, methotrexate, or tripterygium) during 4 weeks prior to screening.
13. Had enrolled in any other trials during 3 months prior to screening or concurrently enrolled in any other trials.
14. Had received previous treatment with any anti-IL-12/IL-23, IL-12, IL-23, IL-17 therapy for the treatment of psoriasis or psoriatic arthritis.
15. Had received natalizumab or any other drugs that regulate B cells or T cells (rituximab, abatacept, alemtuzumab) during 12 months prior to screening.
16. Had received other biologic therapy (e.g., TNF inhibitor) during 6 months prior to screening.