The mathematical model is established for the conventional pump-pipe-injector fuel system. Through the numerical simulations on diesel and DME injection systems, the effects of temperatures on these two injection systems are disclosed, and their differences are illustrated. At the same temperature, line peak pressure and the rate of pressure increase and decrease for DME are lower than that for diesel fuel. Pressure of DME drops 51.1% and 45.2% than that of diesel at 20℃ and 50℃. DME injection rate and cumulative volume flow through nozzle orifice are much lower than that of diesel. The open timing of nozzle is delayed. DME peak rate drops 38.8% and 36.8% than that of diesel at 20℃ and 50℃. With the increase of temperature, the diesel and DME pressures in nozzle, injection rate and SMD all decrease, and the open timing of nozzle is delayed. 