A Lock-Up clutch is installed inside a Torque Converter to improve fuel efficiency. The Lock-Up facing generates heat, and the temperature of the friction surface rises during Slipping Lock-Up. The temperature must be maintained below the acceptable level for ATF (Automatic Transmission Fluid). Therefore, a prediction technics is required at the development stage.Heat flow analysis by CFD (Computational Fluid Dynamics) has been conducted to predict the temperature of the Lock-Up clutch friction surface. In this paper, the target is a Torque Converter with multi plate Lock-Up clutch. An appropriate boundary condition was applied to the flow simulation in order to set the correct total flow rate in the torque converter, and by verifying analysis results, it is confirmed that the prediction of friction surface temperature is close to the data from the experiment. In addition, it is realized that the flow rate has great influence on the temperature of friction surface.Therefore, the analysis which changes the circulation flow rate gradually has been conducted in order to research the magnitude of flow rate effects to the temperature of the friction surface. As a result, it was confirmed that the relation between flow rate and temperature is not in proportion, but at lower flow levels, an increase in the flow results in a greater temperature change than at higher flow levels.From the above, CFD analysis of friction surface temperature during Slipping Lock-Up has led to an accurate prediction, and it has also clarified the influence of flow rate on the facing temperature.