Aiming at the problems of poor stability of conventional PID control algorithm in the temperature control system of morpholine refining tower top, it is not easy to stabilize after being disturbed, the integral separation control algorithm is introduced, Based on Siemens S7 series PLC, the integral separation PID control block program is compiled in the STEP7 programming software, and applied to the temperature control system of the top of the Morpholine refining tower. The result shows that the integral separation PID algorithm effectively reduces the over regulation oscillation amplitude of the system, improves the stability of the control system, and achieves good results in production.