The improvement of the torque converter performance necessitates an optimized design of the torque converter stator blade on the basis of a full understanding of the internal flow conditions. However, it is difficult to analyze the flow experimentally or theoretically because the three elements (a pump, a turbine, and a stator) rotate at different speeds and the flow circuit and the blade shapes are complex. Enough explication of the internal flow has not yet been made.This research has developed a new method of calculating the torque converter performance by taking the stator blade profile into consideration. The internal flow through the torque converter stator can be treated as a two-dimensional flow, and here the flow was analyzed as a potential flow.The analysis of the torque converter stator blade was made as follows. First, the internal flow through the blade row was numerically analyzed by the boundary element method, and the numerical analysis was introduced into the one-dimensional performance analysis. Next, by this calculation method various stator blades were designed and manufactured by way of experiment. As compared with experimental results, it was verified that the torque converter performance can be calculated with satisfactory accuracy.This method was applied with success to optimizing the stator blade shape of the torque converter used for a forklift truck.