The invention relates to an MCR (magnetic control reactor) based reactive power compensation device comprising an MCR, a thyristor, a filter and an SVC (static var compensator) controller. The MCR is connected with the thyristor to form a triangular connection mode and connected on a system voltage bus, and the size of trigger angle control current of the thyristor is changed according to a control command of the SVC controller so as to change saturability of an iron core of the MCR and regulate capacity of the reactor; a filter composed of a capacitor and a switch is connected to the system voltage bus, the input end of the SVC controller is connected with a user PT (potential transformer), a voltage signal and a current signal needed by the controller are collected, the output end of the controller is connected with a thyristor trigger circuit and the switch of the filter, and a control command is outputted. Adopting the MCR, the MCR based reactive power compensation device has the advantages of continuous adjustability in the capacitive to inductive reactive power range, small generated harmonic wave, easiness in maintenance, low cost and the like.