In this paper, based on the high speed schlieren technology, the test observation platform of long gap discharge process and channel insulation recovery process is set up. The synchronization strategy is put forward too. Voltage, discharge current and schlieren pictures observation in the discharge process and channel insulation recovery process are conducted synchronously. Spherical shock wave at the discharge channel and electrode contact point and cylindrical shock wave along the discharge channel are discovered after the long air gap breakdown. Through statistics, the curve of cylindrical shock wave propagation speed and radius of the shock wave, and the influence law of the applying different voltage type to shock wave velocity are obtained.