Abstract: The overload protection mechanism of traditional thermal relay is based on the heated bending properties of double metal sheets. However, because of the double sheet metal materials and characteristics of scattered large, the inverse time characteristic of single, the large error of adjust, poor reproducibility, and it is easily influenced by the environment temperature misoperation or maloperation. So, it is difficult to meet the requirements of the current overload protection. In order to ensure the safety and reliability of the AC motor, it is necessary to study the electronic and intelligent thermal relay. In this paper, a new type of thermal relay control principle is presented, and the feasibility of the principle is verified by experiments. A new way for the motor thermal protection is opened up.