Effectiveness and Safety Study of Solifenacin Succinate and Solifenacin Succinate + Estrogen to Treat OAB in Postmenopausal Women

Inclusion Criteria: * Post-menopausal women aged ≤75. * Signing of ICF. * Willing to and able to correctly complete the urination diary. * Complications of OAB for ≥12 weeks (including: urgent micturition, frequent urination (≥8 times in the daytime, and ≥2 times at the night) and/or urgent urinary incontinence). * No dosing of other drugs of same kind within 14d. -≥8 urination times (24h) in the 1d urination diary. Exclusion Criteria: * Clinically-significant dysuria(at the investigators' viewpoints). * Serious stress urinary incontinence or mixed stress/urgent urinary incontinence (mainly stress one) confirmed by the investigators. * At the ongoing intubatton or the intermittent self-intubatton. * Evidence-based urinary tract infection or chronic inflammation in the recent 2 weeks (e.g. interstitial cystitis), bladder calculus, past pelvic radiotherapy, and past or existing pelvic malignant tumors. * Uncontrolled narrow-angle glaucoma, urinary/gastric retention, intestinal obstruction and other medical symptoms forbidden for anti-cholinergic drugs at the investigators' viewpoints. * Non-pharmacotherapy (including electrotherapy) or bladder training within 2 weeks before the study initiation (or during the study). * Dosing of diuretics and drugs with the cholinergic or anti-cholinergic adverse reactions * Known or suspicious allergy to Solifenacin Succinate, other anti-cholinergic drugs or lactose. * Clinically-significant symptoms inapplicable for clinical study at the investigators' viewpoints. * Participation in other clinical studies within 30d before the random grouping. * No completion of urination diary according to relevant instructions. * Potentially clinically significant abnormalities (PCSA) inapplicable for clinical study at the investigators' viewpoints.