Abstract: Temperature gradient of the side stirred constant thermostatic bath above 100 mm has been studied experimentally. The research shows that the temperature gradient of the upper temperature field of the thermostat bath (30~100) mm can meet the requirements of the general industrial thermometers such as liquid-in-glass thermometer for working and industrial platinum resistance thermometer between 50 ℃ and 200 ℃. According the experiment, the influence of insertion depth on the sensor measurement results depends on the thermal conductivity of the sensor material. The smaller the thermal conductivity is, the smaller the influence will be. For temperature sensors of the same material, the influence of the insertion depth on the measured result depends on the depth-to-diameter ratio. It could be inferred from the experiment that when calibrating the shorter temperature sensor, the axial heat transfer is the main source of measurement errors. As the calibration temperature increases, the insertion depth has a greater influence on the measurement results.