The impedance of ZnO varistor has dynamic characteristics when it is subjected to transient load

thus the dynamic characteristics should be considered in heat dissipating calculation. Based on the nonlinear electro-thermal characteristics of ZnO varistor

the heat dissipation model of the metallic oxide line arrester without gap（MOA） under transient time-varying load is established. Firstly

the change patterns of the ZnO varistor impedance under distinguished loads and temperatures are investigated so as to build a mathematical model of ZnO varistor impedance.Then

the model is substituted into the thermal dissipation calculation module. During the final time-dependent simulation progress

the real-time results are iterated back to the mathematical model

which means the material impedance parameters are adjusted in real time according to the temperature results. Experimental data verify that the calculation results of the heat dissipation model are in accordance with the actual situation. In the case of long heat dissipation time and heat dissipation under continuous operation voltage

the temperature curves of MOA are highly accurate after the dynamic characteristics of the ZnO resistor are taken into consideration.