A torque detecting system for a bottom bracket axle of a power-assisted bicycle includes a torque sensor for being mounted on the bottom bracket axle of the bicycle, a wireless signal transmitter arranged stationarily relative to the bottom bracket axle, and a wireless signal receiver for being arranged at a location of a bicycle frame of the bicycle in proximity to the bottom bracket axle. The wireless signal transmitter is adapted for receiving a detected signal, which is outputted from the torque sensor, and then transmitting the detected signal to the wireless signal receiver wirelessly. In this way, the signal attenuation and the possibility of signal loss of the detected signal can be minimized during the signal transmission, such that the torque applied on the bottom bracket axle by the bicyclist can be detected precisely.