This study is a multicenter, randomized, double-blind, placebo-controlled phase II clinical study to evaluate the efficacy, safety, pharmacokinetics, pharmacodynamics, and immunogenicity of CM512 in subjects with CSU.

Inclusion Criteria:

• Voluntarily sign the Informed Consent Form.
• Age ≥ 18 years old and ≤ 75 years old.
• Patients with a diagnosis of CSU before screening visit, and the duration was ≥6 months.
• Pruritus and wheals existed for more than 6 weeks before screening, despite regular H1-Antihistamines(AH) treatment during this period.
• A stable dose of the second-generation H1-Antihistamines(AH) has been continuously used for at least 7 days before randomization, and the individual is willing to continue to use it stably as stipulated in the protocol during the study period.
• Within 7 days before randomization, UAS7≥16 and ISS7 ≥8.

Exclusion Criteria:

• Not enough washing-out period for previous therapy.
• Planned major surgical procedure during the patient's participation in this study.
• Has ever experienced a systemic allergic reaction or immediate allergic reaction to any biological product (including any excipients).
• CM512 has been used before.
• Women who are pregnant or breastfeeding. During the study period, subjects who had plans to have children, or did not agree to contraception.
• With any medical or non-medical conditions that are not suitable for participation in this study by investigators.