A hoist main shaft torque monitoring device based on angle measurement, constituted primarily by a first base, a second base, a light generating unit, a shutter, and a light sensing element; the light source, a first lens, and a first optical aperture arranged in the light generating unit, as well as a second optical aperture, second lens, and light sensing element on the shutter, forming a light source generation, propagation, and reception pathway; when the elevator main shaft is subjected to a certain torque, a corresponding displacement is produced between the first optical aperture and the second optical aperture, thus measuring the change in amount of light ultimately reaching the second optical aperture so as to measure the twist angle of the rotary shaft and finally calculate the magnitude of the shaft torque. Without damaging the original equipment and foundation, the device measures the torque of the shaft at different rotational speeds. The device can measure stationary torque and torque at different rotational speeds of the shaft, without the electromagnetic field interfering with wireless transmission; the device is easy to use, maintenance costs are low, and it is of interest for widespread popularization.