In view of the structural characteristics of the existing liquid oxygen tank and the technological problems existing in the grinding of the insulation layer of the tank, a grinding device which could be used to effectively and precisely remove the insulation layer material was designed based on the polyurethane foam automatic grinding robot. The device included the grinding tool system, in-situ thickness measurement system and control system. The thickness of the foam layer was accurately measured online through the in-situ thickness measuring system. The straight-line module and the pneumatic motor were used for in-situ position control and speed control of the cutter, respectively. After obtaining the thickness by the in-situ thickness measuring system, the in-situ cutting of the material was carried out at the corresponding position, meanwhile, the effective follow-up dust suction device was assisted to realize the efficient cleaning of the polyurethane foam in the tank.The designed device can not only ensure the processing accuracy, but also greatly improve the working efficiency.