The flat torque converter without inner ring was put forward to find out the impact of different flatness ratios and inner ring on the performance of torque converter. The flat torus design method based on the ellipse was used. Three different flatness ratio torque converters without inner ring were designed. The blade’s profile was distorted in space. The internal flow field of the torque converter was simulated by CFD method, and the distribution of the velocity and pressure of internal flow field was analyzed, so the impact of flatness ratio and inner ring on the flow field and performance could be figured out by analyzing the numerical solution.