Abstract: The characteristics of trace element in mudstone of three wells in the northeastern of Tu-Ha Basin are researched. The results show that the characteristics of trace elements are different in different mudstones formed in different environment. Therefore, the study results can be used to completely recognize the difference between river environment and lake environment. As a result of synthetic study, the palaeo-environment of the Early and Middle Jurassic Shuixigou Group was inferred to be the temperate rainy climate and oxygen-rich fresh water lake. But, from sequenceⅠto sequence Ⅲ, the water body has a trend from brackish water environment to fresh water environment, the palaeoclimate has a trend from semi-aridity climate to temperate rainy.