The crust-mantle structure and magmatic activity is one of the key problems to study the formation and evolution of Southwest sub-basin of South China Sea. According to gravity data supplied by the NH973-1 profile, the authors get the density model of crust-mantle construction with gravity inversion method. And then, the authors learn the temperature structure and thermal evolution consequence after sea-floor spreading. Gravity inversion indicated that there is a deeper sunken sedimentation area and a depressed Moho surface region under the SW sub-basin center. Thermal modeling shows that temperature variation is not a consistent degradation between crust and mantle, but in the way of crust warming with mantle cooling.