This paper optimized the design of the cooling fans of a light-duty diesel engine through numerical simulation. Using Fluent as a platform, a detailed Computational fluid dynamics (CFD) model was developed to simulate both the aerodynamic and the acoustics performance. The model developed was validated against experimental data obtained in this research. The validated model was then used to optimize the design of the cooling fan aiming to minimize the operation noise. With the guarantee of cooling performances, the aerodynamic noise of the two fans has been successfully reduced.