The problem of overheating defect in the valve-side bushing is becoming more and more obvious, the key to solve the problem is to explore the thermal characteristics of the valve-side bushing. In this paper, the thermal loss calculation model was established by analyzing and extracting the current characteristics inside the valve-side bushing, and the dynamic thermal characteristics calculation model of the valve-side bushing defects was established base d on the heat transfer mode of the valve-side bushing, so as to study the dynamic distribution law of the thermal characteristics of the valve-side bushing defects. The results show that the temperature rise of valve-side bushing can be described as a first-order exponential function, this conclusion provides a basis for monitoring the running state of the valve-side bushing.