In response to the problem of sediment leakage from the outflow field during the operation of the trailing suction dredger，we study the outer sediment flow characteristics of the rake head work process.By the numerical simulation method，we analyze the sediment leakage between the front and rear ends of the external flow field of the rake head，and the sediment concentration distribution in the external flow field under different working conditions，and obtain the effect of vacuum and velocity changes on the sediment distribution in the external flow field.The results show that the sediment leakage in the flow field behind the rake head is more serious in the external flow field.The leakages in the vertical and horizontal directions of the flow field are in the form of turbulent flow and laminar flow respectively.The vacuum degree and sailing speed are positively correlated with the leakage amount of the dredge pump.