With the guidance of petroleum system theory, the dynamic filling history of natural gas in the Kela-2 gas field is analyzed by using a large suite of oil and gas geochemistry evidence in combination with the tectonic evolution history and reservoir evolution history. It concludes that the Kela-2 gas field was formed by capturing the gas generated during the main gas generation period, while the late kerogen cracking gas contributed a little to the gas field. It suggests that the gas generated during the main gas generation accumulated in the early-formed wide-gentle anticline, which is the necessary condition for natural gas to re-migrate and enrich late to form the large-scale gas reservoir. The newest research shows that the filling history of gas in the Dabei-1, Yinan-2, Tuziluoke and Dina-2 gas fields was related with the natural gas accumulation in the early wide- gentle anticline as well as late re-migration and enrichment of natural gas.