The invention discloses a three-phase unbalance and reactive power control device and method of an interphase capacitor. The three-phase unbalance and reactive power control device of the interphase capacitor comprises a master controller, a current acquisition device, a voltage acquisition device and a fine reactive compensation unit, wherein the current acquisition device and the voltage acquisition device are connected with an input end of the master controller, and the fine reactive compensation unit is connected with an output end of the master controller and comprises an interphase compensation circuit and a phase-zero compensation circuit. The interphase compensation circuit and the phase-zero compensation circuit adopt capacitors to compensate, the unbalance phenomenon of a three-phase power grid can be effectively controlled; with the utilization of capacitor adjustment branches, the inductive reactive power in three-phase electricity can be effectively offset; and moreover, a plurality of capacitor adjustment branches are connected to the three-phase electricity and between the three-phase electricity and a zero line, the adjustment is more fine, and the over-compensation also can be prevented.