Abstract: The limited ambient temperature is an important indicator for the cooling system of the heavy duty vehicles, which affects the vehicle’s power performance and handling, total lifecycle economic costs, and the reliability of key components. Among them, the type of cooling system fan plays an important role. Taking a heavy duty vehicle as the research object, and using ANSA and Star CCM+ software, this paper calculates the flow field performance of an open fan and an annular fan and establishes a set of mathematical models of the flow field. By analyzing the model characteristics and data advantages, it concludes that annular fans of the same size have higher air volume and better heat dissipation performance than open fans. Finally, a complete vehicle thermal balance test is conducted on a high-power heavy duty vehicle, and the test results are consistent with the simulation analysis results. The performance of the annular fan is better, which provides an effective reference for the matching design of heavy duty vehicle cooling system fans.