Regarding the problem that the internal flow field of the draghead of the rake suction dredger is not clear when excavating clay，the flow field in the drag cavity is simulated，analyzed and optimized. The change of total pressure difference，static pressure difference and cross section velocity of the new and old dragheads are analyzed by using Computational Fluid Dynamics（CFD）value simulation calculation technique. The results show that the vortex area in the drag cavity is reduced，the energy loss is reduced，and the flow performance of clean water is improved. The conclusions are that the streamlined internal cavity of the new draghead makes the internal flow smooth，the transport resistance is reduced，and the cross section velocity tends to be reasonable. Its performance is better than the old draghead.