The suction grille of cutter suction vessels often experiences stone blockage,and the cleaning of stones requires stopping the pump,which is time-consuming and labor-intensive.This article introduces a new type of retractable suction grille,in which each group of retractable suction grilles consists of a fixed inner grille and a movable outer grille.During normal construction of cutter suction vessels,the outer grille is in an upward pushing state under the action of high-speed water flow,and the spacing between the grilles is small.When the stones are blocked between the grilles,the flow rate is reduced to below the critical flow rate,the outer grille drops,the spacing between the grilles increases,and the stones fall off on their own.This article provides a design method for the overall dimensions of the grille,and provides a calculation method for the critical velocity of the upward push of the outer grille and the critical velocity of the detachment of the outer grille and the blocked stone through the theoretical force analysis of the grille and the blocked stone.Furthermore,typical case designs are carried out using theoretical calculations.The grille designed using this method can clean the cutter suction without stopping the pump,effectively improving the efficiency of the cutter suction dredger,and can be used for dredging multi stone soil.