The utility model provides a thickness measurement device of steel under red heat state. Among this measuring device, step motor links to each other with the guide rail lead screw to it moves on the guide rail to drive the slider, the sensor support links to each other with the slider, and two insulation cans are fixed on the sensor support and symmetrical arrangement, install laser displacement sensor and temperature sensor in every insulation can, the insulation can includes inner chamber, insulating layer, water -cooling layer, surveys the window, cools off water course, inlet tube and outlet pipe, and the water -cooling layer sets up at the inner chamber of insulation can outsidely, and the insulating layer setting is in the outside on water -cooling layer, and the water -cooling layer feeds through with inlet tube and outlet pipe respectively, the analysis appearance is connected with laser displacement sensor, temperature sensor and step motor respectively. The utility model discloses a measurement to steel sheet thickness under the red heat state can be realized to the device, and measurement process automation is efficient, has ageingly, can in time discover the thickness problem of steel sheet in producing, the reduction in the number of rejects.