A 400 km-long wide-angle seismic profile in the South China crosses three tectonic domains: southeast continental margin of Yangtze block, northwest continental margin of Cathaysia block, and South China Suture Zone separating these two blocks. The crustal velocity model constructed from traveltime fitting shows that the crust thickness thins from the northwest to the southeast along the profile. It also reveals the crustal contact relationship between the Yangtze and Cathaysia blocks, where the Wuchuan-Sihui fault is the boundary between them. Combining this profile with two more profiles in the continental South China and three profiles in the northern margin of South China Sea, constructs a continent-ocean transition section. This cross-section reveals that the Moho depth shallows gradually along the cross-section from the Yangtze block to the Cathaysia block and the northern margin of South China Sea, but shallows abruptly in the continent-ocean transition to the South China Sea.