Abstract: Regional gravity and magnetic anomaly interpretation shows that many Mesozoic sedimentary basins exist to the north of Xilamulun river in the west out-skater of Songliao basin, and there exists three NW directional deep faults and also some near NEE directional arc structures. Gravity data from 1∶200000 survey can generate clear gradient anomalies of the Mesozoic basin boundaries. Aeromagnetic data at the scale of 1:50000 can be used to outline the distribution of Mesozoic and Cenozoic igneous rock. Integrated gravity, magnetic and MT profile interpretation reveals that thickness of the Mesozoic in this region is from 1km to 4km, and that thickness of Paleozoic can be 4km to 6km. Later Paleozoic thus becomes an important layer for searching oil and gas in this region. Its basement is Silurian and earlier rocks. NE directional distributed garnits in Daxinganling mountain area are mushroom shaped intrusions. With eliminating the affection of igneous rocks in Tuquan and Zhalute basin areas, integrated gravity and magnetic modeling show that Mesozoic thickness variation is from 1.5km to 4km and thickness of the later Paleozoic varies from 2km to 6km.