In this paper, the influence of isolated high-voltage probe parasitic parameters on the cascaded MOSFETs voltage-sharing in traditional voltage-sharing test method is investigated. By changing the number of VDS measuring probes in the same high-side MOSFET, the interference degree of the parasitic parameters introduced into the test method to the transient voltage-sharing is analyzed. On this basis, a test method of voltage-sharing by subtraction is proposed, and its optimization is analyzed and verified by experiments. The experimental results show that the proposed method can accurately evaluate the voltage-sharing ffect of cascaded MOSFETs in steady state and ON/OFF transients , and it is not affeted by the parasitic parameters of the test cable.