The principle of magnetically controlled reactor（MCR） is introduced in this paper

and the relation between the MCR additional winding tap ratio and the harmonic characteristics is analyzed and discussed in accordance with the feature that the control and regulation of the MCR is realized completely by the additional winding. The Matlab simulation software is used for the modeling of the MCR and the simulation result can be used for the reference in choosing the additional winding tap ratio data in the design of the magnetically controlled reactor.