In order to study the influence of different altitude on the performance of vehicle radiator, the simulation model of vehicle radiator was established using FLUENT software. Because of the complexity of radiator structure, the amount of direct modeling and simulation was large. The fins of radiator were regarded as porous media model. The parameters of porous media were obtained by the simulation of radiator unit. The results show that the decrease of air density is the main reason that affects the heat transfer performance of radiator. With the increased of altitude, the atmospheric pressure decreased and the air density decreased, which led to the decrease of Reynolds number and the decrease of convective heat transfer coefficient and heat dissipation at the same time. With every 1000 m rising in altitude, the heat transfer coefficients declined by 4.72%, the heat dissipation decreased by 6.58%.