Abstract: By means of reservior geochemistry,the tight sandstone reserviors of the Middle Jurassic Shaximiao formation (J₂s) in Xinchang gas field,West Sichuan were studied.The chemical mechanism and physical action for formation of internal anisotropy of reserviors were synthetically analysed with the history of tectonic evolution,diagenesis and hydrocarbon migration and accumulation the reservior underwent.Meanwhile,4 types of reserviors were classified according to hydrocarbon producing potential,dynamic character of gas pool and petrologic data,and the most favourable zones for exploration and development were pointed out.