A mid-motor drive system for an electric bicycle, comprising: a left shell, a right shell mounted to the left shell, a motor assembly, a rotation speed reduction apparatus driven by the motor assembly, a crankshaft, a planetary rotation speed increase apparatus driven by the crankshaft, a chainring driven by the rotation speed reduction apparatus and by the planetary rotation speed increase apparatus, a controller connected to the motor assembly for controlling an output power of the motor assembly, and a torque sensor connected to the controller for providing a torque signal to the controller, wherein: the planetary rotation speed increase apparatus comprises a gear ring, a planetary shaft pin, a ratchet fixing seat, an arm, a solar wheel, a ratchet-type unidirectional clutch, and a planetary gear; and the torque sensor is installed on the left shell, and the controller is installed on the right shell; characterized in that the torque sensor comprises a deformation support, a signal transmission module, and a magnetic component, the deformation support is deformed under a force caused by the torque between the left shell and the solar wheel to actuate the magnetic component to move, and the signal transmission module senses the movement of the magnetic component, converts a change of magnetic flux into an electrical signal, and transfers the electrical signal to the controller; and further one of: the deformation support of the torque sensor is an aluminum alloy deformation body, and the magnetic component comprises a plastic support, a steel ball, a spring, a circular magnet, and a plastic slider; and the deformation support of the torque sensor comprises a torque transfer support and an aluminum alloy deformation body, and the magnetic component comprises a plastic external thread shell, a circular magnet, a spring, a plastic slider, and a plastic internal thread fixing support. a left shell, a right shell mounted to the left shell, a motor assembly, a rotation speed reduction apparatus driven by the motor assembly, a crankshaft, a planetary rotation speed increase apparatus driven by the crankshaft, a chainring driven by the rotation speed reduction apparatus and by the planetary rotation speed increase apparatus, a controller connected to the motor assembly for controlling an output power of the motor assembly, and a torque sensor connected to the controller for providing a torque signal to the controller, wherein: the planetary rotation speed increase apparatus comprises a gear ring, a planetary shaft pin, a ratchet fixing seat, an arm, a solar wheel, a ratchet-type unidirectional clutch, and a planetary gear; and the torque sensor is installed on the left shell, and the controller is installed on the right shell; characterized in that the planetary rotation speed increase apparatus comprises a gear ring, a planetary shaft pin, a ratchet fixing seat, an arm, a solar wheel, a ratchet-type unidirectional clutch, and a planetary gear; and the torque sensor is installed on the left shell, and the controller is installed on the right shell; characterized in that the torque sensor comprises a deformation support, a signal transmission module, and a magnetic component, the deformation support is deformed under a force caused by the torque between the left shell and the solar wheel to actuate the magnetic component to move, and the signal transmission module senses the movement of the magnetic component, converts a change of magnetic flux into an electrical signal, and transfers the electrical signal to the controller; and further one of: the deformation support of the torque sensor is an aluminum alloy deformation body, and the magnetic component comprises a plastic support, a steel ball, a spring, a circular magnet, and a plastic slider; and the deformation support of the torque sensor comprises a torque transfer support and an aluminum alloy deformation body, and the magnetic component comprises a plastic external thread shell, a circular magnet, a spring, a plastic slider, and a plastic internal thread fixing support. the deformation support of the torque sensor is an aluminum alloy deformation body, and the magnetic component comprises a plastic support, a steel ball, a spring, a circular magnet, and a plastic slider; and the deformation support of the torque sensor comprises a torque transfer support and an aluminum alloy deformation body, and the magnetic component comprises a plastic external thread shell, a circular magnet, a spring, a plastic slider, and a plastic internal thread fixing support.