In this study, Ex d tube cooled high voltage motor is numerically and experimentally analyzed by CFD(Computational Fluid Dynamics). This motor was designed for explosion environment with pipe cooled. There are two types of pipe cooling methods that are IC611(International Cooling, additional heat exchanger), IC511(International Cooling, heat exchanger in motor frame). In this study IC511 motor is studied that cooling tubes are located in frame. Heat from electric loss is transferred to outside of motor frame by convection, radiation, conduction. Moreover, heat transfer from inner air to external air is occurred through tubes. We tried temperature rise test and compared to get good agreement with CFD(Computational Fluid Dynamics). From the good agreement, we studied several cases of inner flow path. Finally we found optimized size of air path and it led temperature decrease of stator coil.