Abstract: High-resolution seismic data, satellite remote sensing and boring data have been used to examine marine hazardous geologic types and their distribution in the South Yellow Sea. Hazardous geologic map of the South Yellow Sea has been completed. Hazardous geologic types are multiple in the South Yellow Sea, including active fault, earthquake, coastal erosion, coastal accumulation, sand wave, modern tidal sand ridge, palaeo-tidal sand ridge, undersea delta, palaeo-delta, palaeochannel, shallow gas, buried paleochannel, buried palaeo-delta and buried palaeo-lake. The scale of distribution of hazardous geologic types is large. In the sea and coastal area to the west of 122.5°, the types of hazardous geology are much more, and distributed in almost the whole area. Geologic environmental evolution since late Pleistocene decides the formation and regularity of geologic hazards. Three large-scale transgressions happened in the Yellow Sea since late Pleistocene, with two small-scale regressions in between. These processes caused complex marine hazardous geologic types and their distributions. Severe hazardous geologic phenomena will greatly threaten engineering construction and sea bottom stability.We should pay more attention to it.