Abstract: The oil shale of Wulidui Formation in the Wucheng Basin, Tongbai occurs as brownblack, thin and soft slices with an average oil yield up to 6.2%. Many sparsely disseminated and nodular pyrite can be found in the oil shales. With the oil shale occurring in the bottom, trona, salt, dolomite and silty mud rock also the oil shale make up many sedimentary rhythms. The study show that the oil shale was formed in a closed intermountainal basin under muggy climate, stable tectonic environment and sparse supply of terrestrial debrics. Standing water featured by week deoxidizedeoxidize and brackish watersaltwater is suggested for their deposition. Within a prevailing dry, but sometimes with drywet alternated, closed intermountainal basin, the oil shale of Wulidui Formation, together with trona, salt, dolomite and silty mud rock, underwent a climatic variation circle from hothumid →dryheat→ intensively dryheat→dryheat→hothumid.

Key words: Wucheng Basin, Wulidui Formation, oil shale, salt alkali mine, forming environment