The belt tensioning device of the PU timing belt grinding machine includes a driving roller, a frame body, and a power mechanism. On both sides of the driving roller, there are pressing rollers parallel to and close to each other. The left roller support and the right roller support support the active roller. The advantages are: not limited by the circumference of the belt of the synchronous belt, the processing accuracy is easy to control, the belt is simple to load and unload, the equipment is compact, and the production efficiency is high. A belt tensioning device for a PU timing belt grinding machine includes a driving roller (3), a frame body (8), and a power mechanism (1), characterized in that both sides of the driving roller (3) are parallel to and lean against The pressing roller (4) together, both ends of the pressing roller (4) are connected to the pressing roller fixing seat (14); the left support (2) of the driving roller and the right support (5) of the driving roller support the driving roller (3).