Abstract: The Mahai gas field includes Mahai shallow layer tectonic gas accumulation and Mahai deep layer stratigraphic overlap gas accumulation with different accumulation types, forming periods, as well as main controlling forces. Gas of the two accumulations both come from the Yibei depression 40-50 km to the Mahai gas field. Fault and unconformity are the most important paths for vertical and lateral migration. The formation and evolution as well as dynamic features are different, resulting in two kinds of gas migration-accumulation mechanism models: 1)"tectonic stress drives gas to migrate along fault-conduction and forms secondary gas accumulation" for the Mahai shallow layer tectonic gas accumulation; 2)"buoyancy drives gas to migrate along fault-unconformity and forms primary gas accumulation" for the Mahai deep layer stratigraphic overlap gas accumulation. Favorable gas accumulation regions of the Qaidam basin are forecasted according to the two mechanism models.