A central shaft torque sensing system for an electric bicycle having a centre-mounted motor, said system comprising a central shaft, the centre-mounted motor, a sprocket bracket, a controller, a torque sensor, and a strain sleeve, wherein: the controller is connected to the torque sensor and the centre-mounted motor, respectively, the motor comprises a main housing, a coil stator, a motor rotor, a motor output gear shaft, a planetary reduction mechanism and a dual-ratchet clutch, the motor output gear shaft is sleeved on the central shaft and forms an integrated structure with the motor rotor, the coil stator is fixed on the main housing, the motor rotor wraps around the outer side of the coil stator and is fixedly connected with the motor output gear shaft, the planetary reduction mechanism is arranged within the main housing, and the motor output gear shaft engages with the planetary reduction mechanism via a gear, characterized in that one end of the strain sleeve is connected to the dual-ratchet clutch, the other end of the strain sleeve is sleeved on the central shaft and is fixedly connected with the central shaft, the torque sensor is mounted on the strain sleeve, the dual-ratchet clutch is formed by means of two ratchet wheels which have the opposite stopping directions superposing axially and is composed of an inner ring, a middle ring and an outer ring, the middle ring is fixedly connected with the sprocket bracket, the inner ring is connected with the strain sleeve, the outer ring is connected with an output end of the planetary reduction mechanism, wherein i) a part of the inner ring of the dual-ratchet clutch is connected with the strain sleeve via a first spline of which the teeth and key slots present a torque travel clearance fit, the other part of the inner ring slides on the central shaft, or ii) a part of the inner ring of the dual-ratchet clutch is connected with the strain sleeve via a first spline, the other part of the inner ring is connected with the central shaft via a second spline, the teeth and key slots of the second spline present a torque travel clearance fit. the controller is connected to the torque sensor and the centre-mounted motor, respectively, the motor comprises a main housing, a coil stator, a motor rotor, a motor output gear shaft, a planetary reduction mechanism and a dual-ratchet clutch, the motor output gear shaft is sleeved on the central shaft and forms an integrated structure with the motor rotor, the coil stator is fixed on the main housing, the motor rotor wraps around the outer side of the coil stator and is fixedly connected with the motor output gear shaft, the planetary reduction mechanism is arranged within the main housing, and the motor output gear shaft engages with the planetary reduction mechanism via a gear, characterized in that one end of the strain sleeve is connected to the dual-ratchet clutch, the other end of the strain sleeve is sleeved on the central shaft and is fixedly connected with the central shaft, the torque sensor is mounted on the strain sleeve, the dual-ratchet clutch is formed by means of two ratchet wheels which have the opposite stopping directions superposing axially and is composed of an inner ring, a middle ring and an outer ring, the middle ring is fixedly connected with the sprocket bracket, the inner ring is connected with the strain sleeve, the outer ring is connected with an output end of the planetary reduction mechanism, wherein i) a part of the inner ring of the dual-ratchet clutch is connected with the strain sleeve via a first spline of which the teeth and key slots present a torque travel clearance fit, the other part of the inner ring slides on the central shaft, or ii) a part of the inner ring of the dual-ratchet clutch is connected with the strain sleeve via a first spline, the other part of the inner ring is connected with the central shaft via a second spline, the teeth and key slots of the second spline present a torque travel clearance fit. i) a part of the inner ring of the dual-ratchet clutch is connected with the strain sleeve via a first spline of which the teeth and key slots present a torque travel clearance fit, the other part of the inner ring slides on the central shaft, or ii) a part of the inner ring of the dual-ratchet clutch is connected with the strain sleeve via a first spline, the other part of the inner ring is connected with the central shaft via a second spline, the teeth and key slots of the second spline present a torque travel clearance fit.