Objectives：Sichuan Basin is an important salt forming and potassium accumulating basin in China. There are a lot of polyhalite in the Triassic Jialingjiang Formation and Leikoupo Formation， which is characterized by wide distribution， multiple layers and large accumulated thickness. Previous studies on the microstructure and genetic mechanism of polyhalite have little influence on the exploration and deep chemical exploitation of polyhalite in Sichuan Basin.Methods：In this paper， through field investigation， thin section， electron microprobe， quantitative spectral analysis and evaporation test， combined with lithofacies paleogeography and sedimentary geochemistry， the micro fabric characteristics and genetic mechanism of polyhalite are studied.Results：The results show that the distribution of polyhalite in Sichuan Basin is not consistent with that of salt rock. Polyhalite is mainly distributed in Guang'an wusheng， Qionglai Pujiang and Changshou Dianjiang areas. In Sichuan Basin， there are two kinds of K- forming sequences: anhydrite rock salt polyhalite rock salt anhydrite and anhydrite polyhalite anhydrite. The microscopic morphology is mainly as follows: ① it is massive， flaky， aggregate and irregular granular， coexisting with halite and anhydrite; ② it is radial， fibrous and petal shaped; and ③ it is star like， fragmentary and bay shaped， and coexists with anhydrite.Conclusion：Based on the results from the analysis and arrangement for the collected. The results show that polyhalite has two main Genesis: primary deposition and epigenetic metasomatism. The "Anhydrite—Halite—Polyhalite—Halite—Anhydrite" type polyhalite should be directly separated from the saturated potassium bearing brine. The "Anhydrite—Polyhalite—Anhydrite" type polyhalite is metasomatic origin， which has obvious metasomatic residual structure. Potassium gypsum may be used as the intermediate product of metasomatism. In the long process of sedimentary diagenesis， burial deformation， metamorphism and differential uplift， salt minerals will be transformed and remolded， such as dissolution， metasomatism and recrystallization， forming the combination characteristics of salt bearing sections in Sichuan Basin.