Abstract: Objective To ivsestigate the temperature changes of the internal heat needle for treating chronic soft tissue lesion in vitro, and to lay the base for the further study of its temperature characteristics in vivo. Methods Temperatures of the internal heat needle at four sites underlying 42℃, 50℃, 60℃ and 80℃ were measured with a figure-thermodetector when the internal heat needle was heated for 5, 10, 15 and 20 minutes. Results Temperatures of the internal heat needle were divided into three zones. The first zone （temperatures of the tip） was moderate; the second zone （temperatures of the needle body from 2cm to 6cm） was high; and the last zone （temperatures of the needle body from 10cm to the end） was low. Temperatures of the needle body from the tip to 8cm were average, and were close to that preset. Temperatures of the tip were 1-2℃ lower than that preset. Temperatures of the internal heat needle did'nt fluctuate significantly during heating. Conclusion Temperatures of the internal heat needle are easy to control and steady in vitro. Temperatures of the tip are close to that preset.