Numerical simulation on three dimensional flow and heat transfer in the engine compartment is presented in this report. As the feature of construction in the engine compartment is complicated, mesh generation is difficult. Therefore, to solve this problem we maked and used code ‘Pre.M’, which auto-generates Cartesian mesh model with NASTRAN data. And this calculation solver is used Cartesian coordinate commercial code ‘STREAM’. In this way, we could reduce the time of making calculation model. Computation was executed for high speed, low speed driving and idling(0km/h), in which steady, incompressible and viscous flow have been simulated using the standard k-ε turbulence model. We have compared the calculation values with experiment values, and considered the flow and heat phenomena.