The invention provides an oil reservoir gas tightness evaluation method. The oil reservoir gas tightness evaluation method includes the steps that 1, fine oil reservoir description is conducted on a target research area to complete establishment of a geological model; 2, fault blockage capability evaluation is conducted to evaluate the fault leakage position and the risk level; 3, numerical simulation is adopted for fitting production data of the elastic energy production phase, and the change rule of elastic energy along with time is calculated according to an oil reservoir engineering method; 4, the output of dissolved gas in the elastic production phase of an oil reservoir and the stock of dissolved gas in the oil reservoir are calculated; 5, the tightness of the oil reservoir to gas iscomprehensively evaluated according to the deficit and surplus degree of the dissolved gas. In the oil reservoir gas tightness evaluation method, the deficit and surplus degree of the dissolved gas is calculated according to the material balance principle, the tightness of the oil reservoir to the dissolved gas at the initial stage of development is judged according to the deficit and surplus degree of the dissolved gas, and then the tightness of the oil reservoir to other kinds of gas is indirectly judged.