Smart home appliances have penetrated into every household, and the water heater industry is undergoing new changes. At this time, it is urgent to develop an automatic thermostatic system to ensure that the water temperature remains stable. Intelligent water heater using the STC89C52 can automatically adjust the water temperature, and the system control is achieved through the keyboard. The system can set the temperature accurately to 0.1°C and display the temperature value on the display screen. When the temperature set by the system is higher than the actual temperature, the single chip microcomputer controls the relay to power on and heat it up. When the collected water temperature is higher than the set temperature, the relay will turn off, stopping the heating of the water in the water tank. After experimental verification, it is proved that the system has sufficient stability and reliability, with the advantages of convenience, safety, and small size.