In this paper, the simulated model of an GDI system was created for UAV by GT-Power. This cylinder pressure curves obtained by experiment and simulation results were compared to verify the correctness of the simulation model. The impact of the outbreak of the cylinder pressure, torque, fuel consumption, exhaust gas temperature and NOX emissions with ignition timing was analyzed in high-low altitude based on proved GDI system simulation model. The results of simulation can optimize ignition timing parameters of GDI system for UAV, and provide theoretical guidance to improve engine performance in high-low altitude.