The combination of FEM and BEM can adequately bring into play their advantages in the numerical simulation of diesel engine oil pan; its structure vibration and radiated noise were studied. The FE model and semi-anechoic room BE model were built, the improving designs were put forward by simulation statistics from increasing of damp and structure rigidity. The results showed that the high noise was reduced obviously with damp increasing; the calculation results showed that vibration would reduce and the radiation efficiency was increased by the improvement of the structure rigidity. Comparing the results of experiment and calculation, we found out that both of them have the same trend, so the simulation was verified.