The utility model discloses a low-voltage reactive power automatic compensation device. The low-voltage reactive power automatic compensation device comprises a reactive power controller, electric power compensation capacitors, reactors and switches. The electric power compensation capacitors are serially connected with the switches through the reactors 30 and then connected with an electrical network in a parallel way. The input end of the reactive power controller is in parallel connection with the electrical network. The output end of the reactive power controller cooperates with the controlled electric power compensation capacitors in a switching way through the switches. By adopting the high-integration-level reactive power controller to monitor the electrical network data in a real-time manner, the low-voltage reactive power automatic compensation device calculates a compensation amount according to a preset value and further automatically controls the switches to switch a corresponding number of electric power compensation capacitors on to compensate the reactive loss in the electrical network. By adopting the high-integration-level high-reliability reactive power controller, the low-voltage reactive power automatic compensation device is enabled to have the characteristics of simple structure, working stability and reliability, low closing inrush current and obvious increase in the power factor. The power factor is improved. The line loss is reduced. The load capability of the electrical network is enhanced. The power supply qualities are further improved. The energy-saving aim is also achieved.