The invention relates to a tire grinding device. The tire grinding device comprises a positioning mechanism with a positioning head, and a grinding mechanism close to the positioning head. The positioning head is provided with a rotating shaft. A runner is arranged at the end of the rotating shaft. Protruding parts are arranged on the runner in the outer circumferential direction. The outer circumference of the runner is sleeved with an annular air bag. Grooves coinciding with the structures of the protruding parts are formed in the inner circumference of the annular air bag. The air bag is provided with an air nozzle. Protruding patterns are arranged on the outer surface of the air bag, incline by a certain angle in the radial direction of the annular new air bag and extend. The grinding mechanism is arranged on a vertical guide rod, a grinding wheel is further arranged on the grinding mechanism, and the positioning head can be close to the grinding wheel under driving of the drive mechanism. By means of the air bag, a positioning mechanism made of metal or other hard materials is replaced in the prior art, the positioning mechanism conducts full-area fixing on a tire in an inner cavity of the tire, and after the air bag is fully inflated with air, the inner cavity of the tire can be inflated fully through the air bag, and the inner portion of the tire is supported; and during grinding wheel grinding, the grinding position is not prone to being sunk.