A sub-frame cleaning device, comprising: a rack, a water tank, supporting assemblies, a rotating assembly, wherein the water tank is arranged at the bottom of the rack and is filled with a cleaning solution; the supporting assemblies are used for accommodating a sub-frame, there are four supporting assemblies, characterized in that the device comprises: a bottom lifting assembly, a top lifting assembly, and an expanding and cleaning-off assembly, wherein the bottom lifting assembly is fixedly arranged on the bottom surface of the rack and is located in the water tank; the bottom lifting assembly is capable of driving the supporting assemblies on the bottom lifting assembly to move up and down in a vertical direction; the supporting assemblies are arranged on the bottom lifting assembly and are respectively arranged at vehicle body mounting holes in the sub-frame, and the lower end surfaces of the vehicle body mounting holes are tightly attached to the upper surfaces of the supporting assemblies; the top lifting assembly is fixedly arranged at the top of the rack, the rotating assembly is fixedly arranged under the top lifting assembly, the expanding and cleaning-off assembly is fixedly arranged under the rotating assembly, and the top lifting assembly is capable of driving the rotating assembly on the top lifting assembly and the expanding and cleaning-off assembly to move up and down in the vertical direction; the rotating assembly is capable of driving the expanding and cleaning-off assembly located under the rotating assembly to rotate; the expanding and cleaning-off assembly comprises: four expanding assemblies, an air compressor, and a position adjusting assembly; the position adjusting assembly is arranged at the bottom of the rotating assembly and is used for adjusting the positions of the four expanding assemblies to ensure that the four expanding assemblies are in one-to-one correspondence to the vehicle body mounting holes in the sub-frame in position; and the expanding assemblies are capable of deforming to expand to be fixed to the inner walls of the vehicle body mounting holes or restoring to be separated from the inner walls of the vehicle body mounting holes; air outlets are formed in the lower ends of the expanding assemblies, compressed air ports (32, 41, 55, 68) are arranged inside the expanding assemblies, the air compressor is connected with the compressed air ports by compressed air pipelines, the compressed air ports communicate with the air outlets, and compressed air may be blown into the vehicle body mounting holes through the air outlets and may be blown into a cavity of the sub-frame to clean off aluminum scraps and residual sand in the cavity of the sub-frame. a rack, a water tank, supporting assemblies, a rotating assembly, wherein the water tank is arranged at the bottom of the rack and is filled with a cleaning solution; the supporting assemblies are used for accommodating a sub-frame, there are four supporting assemblies, characterized in that the device comprises: a bottom lifting assembly, a top lifting assembly, and an expanding and cleaning-off assembly, wherein a bottom lifting assembly, a top lifting assembly, and an expanding and cleaning-off assembly, wherein the bottom lifting assembly is fixedly arranged on the bottom surface of the rack and is located in the water tank; the bottom lifting assembly is capable of driving the supporting assemblies on the bottom lifting assembly to move up and down in a vertical direction; the supporting assemblies are arranged on the bottom lifting assembly and are respectively arranged at vehicle body mounting holes in the sub-frame, and the lower end surfaces of the vehicle body mounting holes are tightly attached to the upper surfaces of the supporting assemblies; the top lifting assembly is fixedly arranged at the top of the rack, the rotating assembly is fixedly arranged under the top lifting assembly, the expanding and cleaning-off assembly is fixedly arranged under the rotating assembly, and the top lifting assembly is capable of driving the rotating assembly on the top lifting assembly and the expanding and cleaning-off assembly to move up and down in the vertical direction; the rotating assembly is capable of driving the expanding and cleaning-off assembly located under the rotating assembly to rotate; the expanding and cleaning-off assembly comprises: four expanding assemblies, an air compressor, and a position adjusting assembly; four expanding assemblies, an air compressor, and a position adjusting assembly; the position adjusting assembly is arranged at the bottom of the rotating assembly and is used for adjusting the positions of the four expanding assemblies to ensure that the four expanding assemblies are in one-to-one correspondence to the vehicle body mounting holes in the sub-frame in position; and the expanding assemblies are capable of deforming to expand to be fixed to the inner walls of the vehicle body mounting holes or restoring to be separated from the inner walls of the vehicle body mounting holes; air outlets are formed in the lower ends of the expanding assemblies, compressed air ports (32, 41, 55, 68) are arranged inside the expanding assemblies, the air compressor is connected with the compressed air ports by compressed air pipelines, the compressed air ports communicate with the air outlets, and compressed air may be blown into the vehicle body mounting holes through the air outlets and may be blown into a cavity of the sub-frame to clean off aluminum scraps and residual sand in the cavity of the sub-frame.