The invention belongs to the technical field of torque measurement devices, and discloses a flexible photoelectric torque sensor for a flexible manipulator joint, and an application method. An inner ring and an outer ring of an elastic element are connected through two flexible ribs; the flexible ribs are provided with light shielding piece installation holes; light shielding pieces are fixed ontothe flexible ribs; a support seat installation hole is formed in the outer ring of the elastic element; a support seat is fixed onto the outer ring of the elastic element; and photoelectric type displacement sensors are arranged on the support seat and are located in an inner space of the elastic element. According to the flexible photoelectric torque sensor for the flexible manipulator joint, and the application method provided by the invention, the installation directions of the two photoelectric type displacement sensors are opposite, and the corresponding working directions of the photoelectric type displacement sensors are opposite, so that torque information in the two forward and backward directions can be detected; and the elastic element is elastically deformed when being stressed by torque, and a larger torque angle is produced, so that the passive rigidity of a manipulator is effectively reduced, and the flexibility of a robot is improved. According to the flexible photoelectric torque sensor for the flexible manipulator joint, and the application method provided by the invention, the torque measurement of the manipulator in the two forward and backward directions is realized, great flexibility is provided for the manipulator, and the safety in interaction of the robot and the outside is ensured.