Conventional heat transfer fluids used for cooling fluids in vehicle cooling water jacket have relatively poor heat transfer performance.One method for enhance heat transfer in cooling-jacket uses nanofluids. Nanofluids have heat transfer enhancement merits .In the present study, the numerical simulation on Fe3O4 nanofluid flow in cooling water jacket of Gasline direct injection engine wax performed using computational fluid dynamics ( CFD) software FLUENT. The heat transfer coefficient of nanofluids was calculated and verified by experiment. Fe3O4 nano-particles were used in mixture of water/ethylene glycol as a base fluid. The thermal performance of the nanofluid was studied, also the thermal performance of a cooling-jacket was studied with CFD software. The simulation was performed for different volumetric concentrations of(1%,2%,5%) nanofluids of different engine speeds. The results showed that nanofluids enhanced heat transfer compared to the base fluid.But the pressure drop enlarged in cooling-jacket with nanofluids. The heat transfer coefficient enhancement of about 62.5% compared to the base fluid with 5% volume percent, but the max pressure drop about 45kpa in the cooling-jacket.