Abstract: Objective To further understand the incidence trend of communicable diseases in Ninghai county, learn about the underreporting of the communicable diseases in residents, estimate the more accurate incidence level and provide evidence for developing prevention and control measures and eradication programme of communicable disease. Methods The retrospective interview was conducted in the households by stratified random sampling in the county, which was divided into eastern, southern, western, northern and central parts. Results A total of 10 276 residents in 3120 households in 7 townships (street) were surveyed and 149 cases of 9 communicable diseases previously occurring were recorded, of which 38 cases were underreported (25.50%). No underreporting of class A and B communicable disease was found. The reporting rate of class A and B communicable diseases was 241.35/lakh in 2010, the standard rate was 241.35/lakh. The underreporting rate of class C communicable disease was 29.01%. The reporting rate of class C communicable disease was 1066.57/lakh in 2010, the standard rate was 1502.42/lakh. Among 131 cases seeking medical care, 20 were underreported (15.27%), 18 cases received no medical care, and all were underreported (100%). Conclusion Underreporting of communicable diseases was found in the residents in Ninghai and the underreporting rate of class C communicable disease was high. The underreporting rate was higher in floating population than in local population.