Coarse-tuning and fine-tuning adjustment of the power reactor's inductance is very important for the operation of power system. Thus, a theory is proposed that could achieve the coarse-tuning and fine-tuning adjustment of inductance by adjusting the distance between the two magnetic-pillars to change the working magnetic circuits and its reluctance so as toachieve a continuous adjustment of inductance. Combined with magnetic circuit of Ohm's law the calculating formula of inductance could be deduced; modeling reactor's 3D magnetic-field, magnetic flux density and inductances could be caculated by finite element method.And the feature of inductance's adjustment curve is analysed in detail. The results show that the position of moveable magnetic-pillar could change the working magnetic circuit, and the number of working magnetic circuits changes from one to three, then from three to two; the relationship between inductance and the distance of two magnetic-pillars is a double exponential function. When the distance between the two magnetic-pillars increases, the inductance decreases; the inductance's adjustment curve is composed of three areas:coarse-tuning area, transition area and fine-tuning area. The reactor based on this theory could achieve coarse-tuning/fine-tuning adjustment of inductance.