Take the LVQB current transformer as standard capacitor through changing the wire connecting is a new calibrating method for CVT. The changing process is realized by switching the disconnector. During switching the DS, a very high floating voltage maybe produced, which destroys the insulation of the disconnectors and eventually leads to the failure of verification. Therefore, this paper focuses on the generation mechanism and transient characteristics of floating potential. Considering the modification method and the working mode of current transformer, two different equivalent circuits for generating floating potential are established. After analyzing the dynamic response of the equivalent circuit, the transient process of floating potential is analyzed by Laplace transform. According to the results of Laplace transform analysis, the transient process of the system is simulated by MATLAB, and the factors affecting the floating potential are analyzed. The simulation results show that although the transient process of the floating potential is very short (less than 0.03 ms), the high amplitude overvoltage (604.9 kV) produced by the floating potential may still break down the disconnector. The floating potential can be controlled in a safe range by controlling the switching angle. Therefore, the control of the switching angle of the disconnector must be paid attention to when checking.