For the dredging operation of the trailing suction hopper dredger，the suctioned clay is easy to accumulate inside the drag head and cause blockage，which can lead to the problem of the dredging efficiency reduction. We study the structure of the drag head to find that the grille to prevent debris from entering the dredging pump is the main location of clay plugging. Based on the Euler-Euler model，we carry out fluid dynamics numerical study to analyze the pressure and speed of the drag head and obtain the influence of different working parameters and grid angle on drag head pressure，velocity，and sediment concentration. The results show that the low-velocity area inside the drag head is prone to clay plugging，and the high-pressure water jet can increase the local velocity and promote the mixing of clay and water. Moving forward of grille can effectively prevent the drag siltation during the construction clay process，and improve the working efficiency of the trailing suction hopper dredger.