Temperature rise characteristic is the key factor affecting the reliability of overload relay. This paper taked the typical products as an example to study overload relay temperature real-time monitoring system performance based on PIC16F877A MCU. Heat transfer principle of overload relay was analysed to emulate the temperature field, then the temperature monitoring points was selected. The method of temperature rise monitoring was determined, and real-time temperature rise monitoring system for overload relay was designed to realize the real-time monitoring of temperature rise. Compared to the results of theoretical analysis and simulation, the result of the real-time monitoring were basically the same.