Abstract: Gas injection is widely used in heavy oil thermal recovery process and the effect is remarkable, while too much gas injection is easy to cause gas channeling, which will affect the production of adjacent wells and reduce the development effect. Through one-dimensional tube physical simulation experiment and large-scale 3 D high temperature and high-pressure physical simulation experiment for heavy oil reservoir a in Bohai oilfield, the optimization of gas injection quantity is studied. The results show that when the injected gas volume is greater than 0.12 PV, the gas is found at the production end, which is basically consistent with the theoretical calculation results of the field test well. The results provide experimental data for gas injection optimization and gas channeling prevention in advance, as well as provide an important basis for the design of reservoir and process plan.