Aiming at the problem that DC grounding electrode line is easy to build arc between insulator strings when subjected to lightning stroke and operating overvoltage，the chain arc model is adopted to consider the effect of magnetic field force，thermal buoyancy and air resistance on current element，and the relationship between air resistance coefficient and Reynolds number under different moving speeds of current element． The force of current element is analyzed and the motion model of arc is obtained． Through simulation and analysis of the movement of DC arc between sheep － horn electrodes，it is found that there is a correlation between the extinguishing time of DC arc and the magnitude of current and electrode opening angles． The bigger the arc current and the electrode opening angle，the shorter the extinguishing time of DC arc． The simulation research provides a theoretical basis for the subsequent DC arc test．