In order to understand the application effect and control strategy of environmental protection overflow pipe on the actual ship，combined with the actual mud tank size of the trailing suction dredger，the numerical simulation of the green valve in different angles of environmental overflow pipe is carried out by using the homogeneous flow model in CFX，then the air volume fraction in the overflow pipe with different horizontal angle of green valve is obtained. The results show that： 1） The green valve can significantly reduce the air entering the overflow pipe，and the volume fraction of the overflow pipe is significantly reduced when the horizontal angle of the green valve is 30°. 2）The inlet position and the working state of the overflow pipe also affect the air bubble content of the overflow liquid.