In the last decade, deep seismic sounding (DSS) of profiles several ten thousand kilometers in length has been conducted in the mainland of China. A lot of results published in Chinese were compiled and a map of Moho depth was presented in this paper. Coverage of DSS profile is not uniform, and is lacking in some areas, especially in the western part of China. In this case, the results from dispersions of seismic surface waves and other materials were considered. According to the Moho depth, the mainland of China can be divided into eight crustal blocks. The Moho depth is uniform and varies little inside the same block, while it changes abruptly from one block to another. The Tibetan Plateau is characterized by a thickest crust in the world. It may be due to the penetration of Indian crustal materials into the Tibetan crust or upper mantle. Deeper Moho in the neighbouring areas of Tibet may also be effected by the complicated collision processes between the two continents. Thin crust of the North China Plain is considered to be related to the magmatic activities in the lower crust and upper mantle. While the crust of the eastern part of South China may be due to the accretion of terrain from the ocean islands.