The invention relates to a force-sensing operating robot joint torque sensor, in particular to a mechanical arm joint torque measuring device adaptive to an operating robot light mechanical arm soft joint and the relevant field. The device comprises an elastic member, a detecting head and a displacement detecting component. The elastic member comprises an internal ring and an external ring which are connected through elastic ribs. The displacement detecting component is mounted on the external ring. The detecting head is mounted at one ends of the elastic ribs adjacent to the internal ring, corresponds to the displacement detecting component and is capable of moving along the circumferential direction of the elastic member and the detecting direction of the displacement detecting component. The device is simple and compact in structure, small in size and weight, easy to mount, reliable and practical; the detecting sensitivity is high, the rigidity is high, the measuring instantaneity is high, the accuracy is high, and the light mechanical arm joint design requirements are met.