Constant temperature control system is studied in this paper, which is based on AT89S51 produced by ATMEL company as the control core. The characteristic of this system is small volume, low cost, strong function, simple and widely used. The design through the microcontroller control DS18B20 uptake real-time temperature information, the keyboard set temperature, time and state, LCD1602 display method of relevant information, which realizes the design of constant temperature control system based on single chip microcomputer. Finally, experimental results show that the design can realize temperature display, timing system and according to the temperature activate the corresponding functional circuit and other function, which has certain creativity and usability.