Aiming at the large hysteresis characteristic of ammonia vaporization process of a synthetic ammonia process liquid, the basic principle and applicability of Dahlin control algorithm are studied. The mathematical model of the controlled object was obtained by identifying the field production data, use Siemens S7 series PLC control platform,the control program of liquid ammonia vaporization temperature based on Dahlin algorithm is developed, and good control effect is obtained in the simulation experiment, it has good reference significance for engineering practical application.