Dynamic contact resistance measurement（DRM） is an effective technique for assessing the contact condition of high voltage SF6 circuit breaker. Due to fluctuations in dynamic resistance curves

difficulties are often faced in the calculation of the DRM features and the evaluation of the contact condition. The dynamic contact resistance curves of a high voltage SF6 circuit breaker at different wear stages are investigated

and three kinds of fluctuations are found

namely

vibration

narrow pulse（several μs）

and wide pulse（ranged from dozens μs to hundreds μs）. Simulation of the dynamic contact resistance measurement is performed to investigate their mechanism. Conclusions are drawn as follows. The vibration on the resistance curves is due to the relative motion of the contacts in DRM tests

and it indicates the surface condition of the contacts. The narrow pulse is caused by the current commutation from the main contacts to the arcing contact

thus it is the mark of the main contacts separation. The wide pulse is due to the contact bounce and the arc ignition between the arcing contacts

thus it is the mark of the arcing contacts separation. Narrow pulse and wide pulse are key features which are used to determine the separation time of the contacts and to evaluate the contact condition.