Recently, Load of transmission is increased by high performance and high power of commercial vehicle. So transmission for commercial vehicle is required to supply the proper lubricant oil if reducing the worn and heat by great rate. But flor characteristics of oil pump cannot be confirm with experimentation. In this study, we could find out the flow ripple in oil pump which is to supply lubricant oil at lubricant system of transmission. And detailed complex flow of oil pump was examined by numerical analysis.