Visit 2 (Day 0, baseline visit): Patients who fulfil all the study inclusion and exclusion criteria will accept baseline assessment (including concomitant medication, vital signs and scale assessment) and be randomised into paroxetine CR plus IBS regular treatment group or IBS regular treatment only group at baseline visit. The day after randomizing (Day 1), patients will receive paroxetine CR 12.5mg/d plus IBS regular treatment or IBS regular treatment only (patients who have received IBS regular treatment before can continue their treatment). On Day 8, following 1 weeks of treatment, paroxetine CR should be titrated to 25mg/d.