Automatic Transmission is controlled by pressure of ATF(Automatic Transmission Fluid), and is composed by many rotating components. Part of components is under ATF and it causes rolling resistance when it is rotating. Also collision between ATF and rotating components makes the air bubbles which are included in ATF, so they increase the oil level and driving loss. In this study, shape design of the Oil Pump Chain Cover was performed to improve the oil flow and reduced the air content. Finally, decreased air content was confirmed by experimental measurements and reduced driving loss was evaluated.