Abstract: The mass transfer coefficient distribution between the pipe wall and fluid was simulated by the k-ε model of computational fluid dynamic method. The distributions of flow accelerated corrosion (FAC) rate in downstream of orifice pipe were calculated by Sanchez-Caldera model. The results show that the sensitive position of FAC moves to downstream as decreasing orifice diameter ratio. However, the increase of inlet velocity has no significant influence on sensitive position of FAC. The FAC rate can be effectively reduced with increasing pH value.