A break arc is generated in a DC48V and 9A resistive circuit for different contact opening speed.The speed is changed to 10ram/s, 20mm/s and 30mm/s.While the break arc is maintained, the morphology of the cathode surface and motion of the break arc are observed by two high-speed cameras, simultaneously.The expanding dark region formed on the cathode surface is observed by means of spectroscopic imaging technique.The time evolution of the size of the dark region is investigated for each opening speed.Results are shown as follows.The diameter of the dark region increases linearly while the break arc is maintained.The size of the dark region increases with decreasing the opening speed.There are three regions on the cathode surfaces for all contact opening speed.The ratios of areas of these regions changed for each speed.