Xing Northeastern Sichuan Basin - Feixianguan is found in China in recent years, an important gas reservoirs, recoverable reserves have reached about 5 000 ?108m3, Northeast Sichuan has become the focus of China's oil and gas exploration areas. The trace element analysis by its dolomite, dolomite to explore its causes. Changxing - Feixianguan Sr, Mn, Fe element content are located at 80 ~ 500 μg / g, 7 ~ 90 μg / g, 0.6% ~ 1.4% between the average values of 140μg / g, 60 μg / g, 0.7%, high Sr, low Fe, Mn nature, they can prove that deposition, diagenetic no involvement other than fresh water, but also shows the origin of dolomite instructions. It can be ruled out because of the mixed water into clouds, to support prospective students with burial dolomitization mechanism.