The present application relates to an on-line automatic detection device for wheel brake space, which is composed of a lower lifting drive system, a detection system, a synchronous clamping drive system and an upper driving and pressing system. In use, the device may not only detect the brake space of the back cavity of the wheel, but also detect the specific value of the interference amount of the brake space. Moreover, it has the characteristics of high automation, powerful function, advanced technology, strong versatility, and safe and stable performance.