Abstract: The abnormal heat problem of reactor envelope is serious, leading to insulation failure and equipment damage. For timely detection of abnormal heat, a reversible temperature indication method using coating test is proposed to identify the thermal defect of dry hollow reactor. The colour change properties and the electrical and thermal properties are also studied and analyzed. The results show that the color shade of color changing material is determined by Bisphenol A color developer. The color first darkens and then slowly lightens as the content increases. The color change temperature is based on the polypropylene wax solvent. The higher the content is, the higher the temperature at the beginning of color change will be, which is not obvious at the end of color change. Based on the color change, color change time, recolorization time, color change temperature and reversibility of material, the best ratio of components (crystalline violet lactone, bisphenol A, polypropylene wax) are obtained. For temperature indication coating produced by stirring and mixing, the color change temperature ranges from 107 ℃ to 113 ℃. The color change is obvious, and it has good acid-alkaline resistance and organic solvent. With increasing component content of color changing material, the flashover voltage along surface increases and then drops, and it reaches the peak of 9.27 kV/cm when PRTV to colour change material mass ratio of 10:3.4. The thermal conductivity ranges 0.2514~0.5806 W/(m·K), which decreases as the component content of color changing material increases. Consequently, a reference for the temperature online detection of thermal defects in dry hollow reactor is provided.