Abstract: The Mesozoic of the Nansha block of the southern South China Sea has suffered various degrees of compression in addition to a strong denudation by the end of Mesozoic. Multi-channel seismic data are interpreted to reveal the characteristics and genesis of the Mesozoic tectonic deformation. Tectonic restoration was conducted to remove the Cenozoic deformation and at the same time the Mesozoic tectonic compression ratios were calculated. Through them we found that there were two compressive stresses coming from opposite directions, one from S(S)E and another from N(N)W. The strength of the stresses decreased from the west to the east and from the north to the south. The variations in compression ratios may be related to the opening of the proto-South China Sea and the change in drifting rate of the Nansha block northward.