Multiphase unconformities were found in the Bamianhe area of Dongying sag. The unconformity in the bottom of the Kongdian formation is very important for petroleum accumulation in this area. Seismic section was comprehensively interpreted to discover three unconformity types including truncation-overlap unconformity, parallel-overlap unconformity and truncation-parallel unconformity. According to the log data analysis, the unconformities were divided into three parts vertically: rocks deposited above the unconformity interfaces, weathered clay layer and semi-weathered rocks below the unconformity interfaces. Under the weathering and leaching action，the permeability of semi-weathered rocks is improved. Based on the combination of different unconformity types and lithologic configurations, 12 lithological combination types were proposed, which play different roles in the oil and gas migration and accumulation. The exploration has proved that numerous oil and gas shows and petroleum accumulations exist within 40 m range both above and below the unconformity interfaces. The stratigraphic overlap reservoirs can form above the unconformity interfaces in the area where the truncation-overlap and the parallel-overlap unconformities develop combined with sand-mud lithologic configuration; the buried hill reservoirs can form below the unconformity interfaces in the area where the truncation-overlap and the truncation-parallel unconformities develop with mud-sand lithologic configuration.