Abstract: As an important parameter for the electrical contact performance measurement，the size of contact re-sistance is directly related to the operation of electrical equipment． At present，the contact resistance is usually measured with the off-line experimental measurement method，but the measurement result often differs from the ac-tual operating state to a certain extent． So a method for calculation the contact resistance of contact surface based on the axial thermal circuit model was proposed． Firstly，an axial thermal circuit model was constructed taking the contact terminal of overhead ground wire and armor rod as the research object，and the thermal parameters of the model were obtained by genetic algorithm． Then，based on the calculation results of the GJ-50 overhead ground wire，the variation laws of thermal parameters of the model and contact resistance were discussed and analyzed．The results show that the AC contact resistance corresponding to different temperature during the transient tempera-ture rise of contact surface could be obtained accurately by using the proposed method． The contact resistance de-creases with the increase of load current under the steady state temperature，but it is not affected by the time calcu-lation step． The calculation method shows a high accuracy，and the maximum error between the experimental measurement results and the calculation results of contact resistance does not exceed 9%． In addition，the calcula-tion result is more accurate when the relationship between contact resistance and temperature is expressed by the formula proposed by Paulke et al．

Key words: contact resistance, axial thermal circuit model, contact surface, overhead ground wire, armor rod, genetic algorithm