The invention discloses a non-contact piston temperature measuring device which comprises an infrared temperature sensor, a glass window, a water cooling protective cover, an encoder, a piston, a display, a crankshaft, a controller, a connecting rod and an internal combustion engine cylinder body. The glass window is arranged on one side of the side wall of the internal combustion engine cylinderbody, the infrared temperature sensor is arranged at the top of the glass window, the water cooling protective cover is arranged outside the infrared temperature sensor, the piston, the controller, the connecting rod and the encoder are all arranged inside the internal combustion engine cylinder body, the piston is movably arranged inside the internal combustion engine cylinder body, one end of the connecting rod is connected with the piston, the other end of the connecting rod is connected with the crankshaft, and the encoder is arranged at one end in the axial direction of the crankshaft. According to the non-contact piston temperature measuring device, the problems of easy falling off and short service life caused by unstable installation of detectors on the piston in the prior art aresolved.