Based on the AVL FIRE code， the simulation of injection and mixture of natural gas and diesel fuel in a natural gas engine with pilot injection was carried out to study its combustion and emission performance. The related turbulent model was verified by the bed test and then the characteristic parameters， such as orifice position， inclined angle and gas diesel over lapping angle were analyzed. Results show that the k-ε turbulent model is more suitable for simulating the dual fuel injection， and the larger the injection height， inclination angle and over lapping angle， the smaller SMD. In particular， using a large over lapping angle can obtain the best atomization effect. The relative nozzle position will decide the energy transfer between the fuel and gas jets， thus influencing the penetration distance of fuel and gas and the atomization effect.