In this paper, blast effect of oil-associated gas in gas injection wells is determined when using air injection displacement, and on this basis, the relevant safety distance is determined also. Numerical simulation is used to calculate the overpressure distribution, explosion energy and TNT equivalence of combustible gas explosion in gas injection wells. Based on shock wave damage criterion, the safety distances in seven levels are obtained, which are personnel minor injuries, severe injuries, death, and destruction of buildings with mild, moderate, severe manage and destroying. Therefore, technical support is provided to accident prevention, emergency and rescue.