As a potential oil and gas reservoir,reef complexes have been a research focus from petroleum geologists for a long time.There are favorable conditions for the development of reef complexes in the South China Sea; however,their internal structures,evolution and distribution are still poorly understood.Based on 2D and 3D seismic data,the internal structures and evolution patterns of the reef complexes on the carbonate platform margin in the deep water areas over the western South China Sea were studied in detail.The result shows that two types of reef complexes,i.e.,fault controlling platform margin reef complexes and ramp reef complexes have been developed in the study area.The reef complexes have independent or continuous mound or lenticular seismic reflections,with three internal structures(i.e.,aggrading,prograding and retrograding structures).There are different growth rates during the evolution of the reef complexes,resulting in the formation of catch-up reefs,keep-up reefs and quick step reefs.The study also reveals that different platform margin reef complexes have different internal structures and distributions,because of the different platform types.These results may be applied to the exploration and prediction of carbonate platform margin reef complexes in other areas that are similar to the study area. As a potential oil and gas reservoir, reef complexes have been a research focus from petroleum geologists for a long time. Here are favorable conditions for the development of reef complexes in the South China Sea; however, their internal structures, evolution and distribution are still poorly understood. Based on 2D and 3D seismic data, the internal structures and evolution patterns of the reef complexes on the carbonate platform margin in the deep water areas over the western South China Sea were studied in detail. The result shows that two types of reef complexes, ie, fault controlling platform margin reef complexes and ramp reef complexes have been developed in the study area. the reef complexes have independent or continuous mound or lenticular seismic reflections, with three internal structures (ie, aggrading, prograding and retrograding structures). There are different growth rates during the evolution of the reef complexes, resulting in the formation of catch-up reefs, keep-up reefs and qu ick step reefs.The study also reveals that different platform margin reef complexes have different internal structures and distributions, because of the different platform types. these results may be applied to the exploration and prediction of carbonate platform margin reef complexes in other areas that are similar to the study area.