The Boxing Fault is the boundary fault separating Boxing sag from the west of southern slope of Dongying sag.Some wells，with no evidences of oil and gas or showing thick layer of oil and gas but only yielding water in oil test，were drilled adjacent to the thrown side，while heavy oil was only found in Jinjia oilfield at the upthrown side currently. This indicates that the Boxing Fault experienced tectonic activity after the accumulation of oil and gas，which destroyed the palaeooil reservoir，and then some of CO2 were trapped there forming gas-bearing reservoirs. In this paper，Well Gao95 and Fan54 and the neighboring Huagou gas field in the upthrown side of Boxing Fault were taken as examples to analyze the opening and sealing properties of the fault and its control on palaeo-oil reservoirs. Based on the origin of mantle-derived CO2 gas reservoir，the accumulation period of organic CH4 and inorganic CO2 of Well Hua501 and Hua17 in Huagou gas field was analyzed. The obtained results show that organic natural gas and palaeo-oil reservoir found in Huagou gas field and the upthrown of Boxing Fault were formed in the depositional period of Guantao-Minghuazhen Formation of Neogene and the accumulation of CO2 gas reservoir happened in the Quaternary period from 2 Ma to now. The whole process can be characterized as reservoir destroyed first and CO2 gas reservoir preserved later. In the early depositional period of Guantao-Minghuazhen Formation，Boxing Fault was sealed when palaeo-oil reservoirs developed in the third member of Shahejie Formation；and then in the middle depositional period of Minghuazhen Formation，palaeo-oil reservoirs were destroyed when basalt erupted；in the late depositional period of Minghuazhen-Pingyuan Formation，the fault activity stopped and effective traps were connected to mantle source. According to the analysis on the correspondence between the fault activity and the formation time of inorganic CO2，it is concluded that the period of volcanic eruption was the time for inorganic gas accumulation but nor for trapping. Mantle derived inorganic gas migrated upward along the faults and into the favorable traps for accumulation while volcanic activity was quiet.