Objective To investigate the prevalence and distribution of mental disorders among people aged 18 and over in Wuxi， so as to provide scientific evidence for mental health planning in Wuxi. Methods Multistage stratified cluster random sampling method was used to investigate the population of 18 years old and over in Wuxi. The investigation objects were divided into high risk， medium risk and low risk of mental illness groups by the general health questionnaire survey. The Structured Clinical Interview For Diagnostic and Statistical Manual of Mental Disorders-Ⅳ（ DSM-Ⅳ） Axis I Disorders（ SCID-Ⅰ）， DSM-Ⅳ and the mental retardation/dementia scale were used as diagnostic tools to carry out structured clinical interviews in 100% patients from the high risk group， 40% from the medium risk group and 10% from the low risk group， in order to give diagnosis to various of mental disorders. Results A total of 6 263 people completed the screening and 1 128 completed the diagnosis. The current prevalence rate of mental illness was 12.26%. In addition to organic mental disorders， the highest prevalence was anxiety disorders（ 3.45%）， followed by mood disorders（ 1.89%） and substance use disorders（ 1.33%）. Conclusions The prevalence of mental illness in Wuxi has increased significantly. It has become a common disease and a major public health problem urgently needed to be solved.