The invention discloses a control device and a method for controlling chaos based on reactive compensation, which comprises a high potential plate and a thyristor controlled reactor, and further comprises a central processing unit, a reactive compensation unit, a chaos control unit, a power source and a communication module; wherein the central processing unit comprises a sampling module, a preprocessing module, a detection single chip microcomputer, a memory module and a comprehensive treatment single chip microcomputer; the reactive compensation unit comprises a reactive compensation processor, a reactive compensation controller and a feedback sampling module I; the chaos control unit comprises a chaos control processor, a chaos control controller and a feedback sampling module II. The method includes: collecting three phase phase voltage instantaneous values and three phase line current instantaneous values; calculating power grid operating parameters; judging signal anomaly parameters, sending the power grid operating parameters and judging signal anomaly parameters to a liquid crystal display (LCD) to display; and controlling the thyristor controlled reactor to output reactive power. The control device can monitor the power grid operating state in real time, the safety of the reactive compensation is improved, and damages caused by inappropriate compensation of the reactive power to the power grid are decreased.