The present invention relates to a device for low-temperature test of valves, in particular to a plugging device for low-temperature test of back-blowing valves, and also to a plugging method for low-temperature tests of back-blowing valves based on the above-mentioned device, so as to solve the problems of the prior art. After the cryogenic treatment is completed, the residual liquid in the valve cavity will affect the measurement results of the low-temperature sealing test. However, the current method of treating the residual liquid in the valve cavity is low in efficiency and cannot obtain accurate measurement values. The technical solution adopted is a back-blowing valve low-temperature test plugging device, which has a blocking plate, and the blocking plate is provided with a first joint, a second joint, a third joint, and a back-blowing pipe. liquid. The present invention also provides a low-temperature test plugging method for back-blowing valves, including four steps of installing a plugging device, degassing by cryogenic treatment, blowing off residual liquid, and low-temperature sealing test, so as to complete the low-temperature sealing test of the test valve body.