Although the Tarim basin contains rich oil/gas resources, the exploration of oil/gas buried in its deep layers is just beginning, requiring detailed geophysical investigations. This paper presents the results of magnetotelluric investigation for 3D structures within the Tarim Basin. We completed the survey at 701 stations and performed data processing and 3D inversion, obtaining 3D electrical resistivity model of the basin, which shows structures of sedimentary layers from viewpoint of electrical properties. Electrical resistivity of clastic and carbonate rocks in the basin varies in a large range and is mainly controlled by fluid contents contained in pores and cracks. On a plane with a certain depth, structural highs beneath the Jurassic strata usually shows higher electrical resistivity, while lower electrical resistivity zones show information of fluid convergence and strata containing possible oil/gas reservoirs, as oil/gas reservoirs are usually accompanied with vivid fluid motion and fluid is of low electrical resistivity. The inversed 3D electrical resistivity model indicates that the most areas of the upper part of the basin are of low electrical resistivity, caused by the Mesozoic and Cenozoic water bearing clastic rocks. Some local areas with high electrical resistivity coincide with positions of low geothermal heat flow and high density disturbance, reflecting local structural highs. In the lower part of the basin with depth from 6km to 10km, the area of low electrical resistivity is reduced downward, but remains at least 200,000 km2 on the plane of depth 10 km. Based on the idea that lower electrical resistivity zones show fluid convergence and strata containing possible oil/gas reservoirs, the lower electrical resistivity zones revealed on the inversed images from 6km to 10km demonstrate the prospect areas in the deep layers of the basin oil exploration. The prospect areas include the northern Manjar depression to western Tarbei uplift, the Hetain and Sache depressions, as well as the Yutain Mingfeng and Tangguzibas depressions that shows relatively low electrical resistivity on the plane of depth 6~10 km. The crystalline basement can be divided to 3 types as follows : the normal craton basement of high electrical resistivity, the water bearing cracked metamorphic basement with low electrical resistivity, and the basalt intrusive basement with high electrical resistivity.