The invention discloses a decoupling method for using a capacitive sensor to measure transient voltage of a transformer coil. When the capacitive sensor is utilized to measure the transient voltage of the transformer coil, a measurement result is inaccurate due to the fact that the capacitive sensor is adjacent to the coupling effect of the coil. Measured data are needed to be decoupled. The decoupling method comprises the following several steps of establishing a transformer coil equi-dimension model, obtaining a coupling coefficient matrix through an experiment, utilizing capacitive sensor arrays to measure the data and solving a system of linear equations to obtain transient voltage distribution of each pancake of the coil.