Water knife is a kind of environmental protection with high precision cutting tools, use water knife cutting groove configuration, so as to undertake cutting produced in the process of water, sand and debris, and absorb water knife cutting energy of the water column. The cutting groove capacity is limited, and the residue in the tank is required to be removed periodically to ensure the safety of the cutting operation. The sand grains and debris in the cutting groove are mainly from the abrasive (garnet sand) added in the high-pressure water column during the cutting process and the debris produced by the cutting. At present, the method of removing the residue of cutting groove is mainly based on manual excavation and suction pump. The method of manual excavation must first drain the water and then remove the residue with manpower. The pumping method is used to separate the water and residues from the cutting tank to the designated place for settlement and separation. Sometimes it is difficult to clean up. Because of the high dust content in the sand, the effect of adhesion is strong (advice when choosing sand, put sand in a glass, mix the sand and water in a certain proportion, shake, turbidity) overall this method is quite space. Use the sand extractor to remove the residue of the cutting groove, improve the efficiency of the separation of the residue and water, and save space use. It can effectively eliminate the solid particles with particle size of 0.02 mm or above, and the removal efficiency of mud sand can reach 99%. In addition, it can shorten the processing time of water sand separation, increase the reuse of water and save the operation space of residue processing when the pump backflow outlet is located in the opposite position of the pump.