[ Abstract] A numerical simulation on the flow fields of a cabriolet and its hardtop variant is conducted with CFD technique, being verified for its effectiveness. With consideration of the influences of front end intake flow, in-ternal flow field and ground effect, the exterior flow field of two car variants are obtained. It is held by the compara-tive analysis on their flow field characteristics that the mechanism causing the higher aero drag of cabriolet is mainly the uncontrolled trailing of the low-pressure separated bubbles and flow-back vortex in compartment area toward rear end. The proper styling change of windshield and rear end results in the effective control of separated bubbles and flow-back vortex, and hence a 16% reduction of aero drag. The analysis on the mechanism of cabriolet's aero drag in this paper provides an important basis for the styling and aerodynamic performance optimization of cabriolet.%采用经过有效性验证的计算流体力学方法，对某敞篷车及其硬顶变型车进行流场数值模拟。计及前端进气、内流场和地面效应的影响，得到了敞篷车与硬顶车的外流场。通过敞篷车与硬顶车流场特性的对比分析认为，敞篷车较大风阻的产生机理主要在于座舱区域的低压分离气泡和回流涡旋不受控制地向车尾拖曳。通过适当改变敞篷车前风窗和车背造型，有效控制分离气泡和座舱回流，使风阻降低了16%。文中对风阻产生机理的分析，为敞篷车造型设计与气动性能优化提供了重要的依据。
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