Abstract: Multi-channel seismic data are interpreted with the support of drilling and trawling samples from surrounding areas to identify Pre-Cenozoic strata in the middle-west block of the western South China Sea. Results suggest that the Pre-Cenozoic strata do occur in the north of the study area. Upon this fact, the tectonic deformation of the Pre-Cenozoic strata is reconstructed using the back-stripping method, the fault-recovery method and the antitone structural analysis method. The strata can be divided into upper, middle and lower structural layers in the study area. Compressive structures, such as folds and thrusts, are found in the lower structure layer. By the end of Pre-Cenozoic, the region was suffered from continuous gently folding. Combined with the fault thrust direction, it is concluded that the main compressive stress came from the southeast direction, which may be related to evolution of the paleo-South China Sea.