Abstract: The original temperature control system in sink-type stem conditioner was affected by the fluctuation of water level greatly, which resulted in the fluctuation of water temperature and further the temperature of and moisture content in output stem. By analyzing the reasons causing the fluctuation of water temperature, the water supply, drain and heating pipelines were improved, instead of limit control, PID closed loop control was used for controlling water level and temperature. The results showed that the periodic fluctuation of water level was avoided and the water temperature became stabler. A comparative test of water temperature of 60℃ indicated that the temperature difference reduced from ±5.52℃ to ±1.43℃ and the standard deviation from 1.02℃ to 0.62℃. The precise control of water temperature ensures the stability of temperature and moisture content of output stem and fulfills the technical requirements of cut stem production.