The effect of ambient condition on the atomization characteristics were numerically simulated by using centrifugal nozzle as the research object, the influence of ambient air pressure and temperature on atomization characteristics parameters such as oil film thickness and atomization angle were obtained.With the FLUENT used,when the injection pressure was 4.0 MPa, the fuel temperature is 100 ℃,the ambient temperature from －50 ℃ to 400 ℃and the ambient pressure in the range of 0.1～3.0 MPa were numerically simulated.The results show that when the ambient pressure is constant, the temperature increases, the air density decreases, the fuel evaporation intensifies, the gas phase fuel ratio increases, and the atomization effect increases. When the ambient temperature is constant, the environmental pressure increases, the air density increases, the crushing occurs earlier, the oil film thickness increases, and the liquid phase fuel ratio increases, although the spray cone angle and the interaction between oil and gas increase, but it is not conducive to fuel atomization.