A magnitude 8.0 earthquake struck China's southwestern Sichuan province on 12 May 2008. The reported rates of depression symptoms across studies were not consistent, and its protective factors were unknown. This study collected data from Wenchuan earthquake survivors to estimate the prevalence of depression and explore the protective effects of social support and support source on depression. A randomized sampling cross-sectional survey based on community was conducted in January 2009, in Mianzhu and Anxian counties, and 633 survivors were entered into the study. The Chinese edition of the Center for Epidemiologic Studies Depression Scale and the Social Support Rating Scale were used to investigate depression and social support. The prevalence of probable depression in adults 6 months after the Wenchuan earthquake was 22.9% (145/633). Total social support, subjective support, support use and support from family members, neighbours and organizations negatively predicted depression. According to the results, depression was common 6 months after this major disaster. Total social support, subjective support, support use and support from family members, neighbours and organizations were all protective factors for depression after a major disaster.