Abstract: The complexity of sedimentary basins of China is mainly manifested in the following nine aspects:(1) large number, small size and wide distribution;(2) a great variety of basin types;(3) prevalence of the phenomenon of multi-stage basin superimposition and compounding;(4) dominance of continental sedimentary basins;(5) occurrence of numerous, very active faults;(6) strong reworking in the late stage;(7) repeated and extensive magmatic activities;(8) rapid filling rate and migration of most depocenters;(9) inhomogeneous space of the geothermal field.On the basis of this analysis, the authors analyze the origin of the complexity of sedimentary basins of China and point out that the special tectonic position, small and less stable continental block, large-scale and active mobile belt and complex plate tectonic framework and tectonic evolutionary history are the root-causes for the complexity of sedimentary basins of China and caused these basins to have their distinguishing characteristics of petroleum occurrence.