Abstract: Located in the southwestern part of the East China Sea continental shelf basin, the Lishui-Jiaojiang sag is a Cenozoic fault depression with typical east fault and west overpassing characteristics developed on the basis of the Mesozoic residual basins,and it is a new area for oil and gas exploration. Due to the complex geological conditions in this area such as the superimposed structure and the sedimentary thickness, the useful reflection data are not available through seismic exploration. The authors adopted the combination of gravity and magnetic data that are used for a wide area and large depth with seismic data to describe the structure, igneous rock,and lithological characteristics of the basement, and divided the regional faults by using the step boundary recognition technology of gravity and magnetic data. The inner faults in the sag show a north-eastward distribution, which control the shape of the sag. The fault depression is characterized by many small secondary depressions formed by the faults. The Mesozoic and Cenozoic igneous rocks have high gravity and magnetic anomalies. We obtained the strati-graphic, igneous and lithology distribution characteristics from the seismic profile with good quality,and established the formula for the calculation of the mulch-continuous domain strata. The Mesozoic strata are relatively developed in the region, and there are less Mesozoic and cenozoic igneous rocks in the sag, which will not cause the great damages to oil and gas structure. Therefore, this sag has a good oil and prospects.

Key words: Lishui-Jiaojiang sag, gravity and magnetic, fracture, multi connected domain strata, igneous rocks