Based on the working conditions of a cutter suction dredging robot，this paper uses Fluent software to create a cutter suction model，so as to numerically simulate the over and under cutting processes of the cutter under different cutter suction parameters.The paper analyzes the sediment concentration distribution at the entrance of the duckbill tube and the key section of the cutter and studies the flow field characteristics of the cutter during the over and under cutting processes，providing a theoretical basis for the reasonable selection of cutting speed of the cutter for the underwater dredging robot.The findings suggest that during the cutter suction process of the dredging robot，the phenomenon of sediment backfilling is more pronounced during over cutting，while the phenomenon of sediment squeezing is more pronounced during under cutting.It is not advisable to operate the cutter at a high speed during the cutting process，as high-speed cutting can cause unstable sediment concentration during pumping.For low-level pumping flow rates，the cutter speed should be controlled at 15-25 r/min，while for high-level pumping flow rates，the cutter should be controlled at 25-35 r/min to improve productivity.Furthermore，the paper recommends not to arrange the duckbill tube symmetrically but to install it at a certain angle along the rotation direction of the cutter，so as to improve the efficiency of sediment suction.