Abstract: Up till now, China (Taiwan province not included) has discovered 33 large and middle gas fields (each of them has a reserve of≥10×109m3).The total proved reserves of these fields count 72% of the national proved reserves. This paper chiefly discusses the main controlling factors of large and middle gas fields in China ,i.e., they are: developed in gas generating center and /Or its surrounding areas; occurred in paleo-uplifts within the gas generating area, and in buried low, middle coal series or related traps above or beneath them; of late reservoir-forming period possessing large-area porous reservoirs and good regional cap rock. Based on these controlling factors, this paper gives comprehensive evaluations for Tarim, Junggar, Turpan-Hami, Qaidam, Ordos, Sichuan, Yinggehai, Qiongdongnan and Donghai basins. It also points out the exploration plays for discovering large and middle gas fields.