Based on the sequence classification of Wenchang and Enping formation, the activity intensity of main fault in Xijiang main sag was analyzed. And the tectonic evolution of main sections was also studied according to the balanced section technique. It"s believed that, firstly, the fault number F1 in NE direction was a regional sag-controlling fault, and it had very important influence on the sedimentary filling and tectonic evolution; secondly, most of the main faults had a strong activity intensity in Wenchang stage while weak in Enping stage; thirdly, the tectonic evolution of Xijiang main sag could be divided into four stages, which begun with starting fault-depression stage, and followed strong fault-depression stage, fault-sag transition stage, thermal subsidence stage. Among the four stages, the stage of starting fault-depression and strong fault-depression were significant for the formation,enlargement and sedimentary filling of the Xijiang main sag.