The invention discloses an on-line monitoring early-warning device for an SPD, and the device comprises an operation statistics module, an inrush current sensing module, a voltage sensor, a current leakage sensing module, a temperature collection module, and a processing module. The processing module is connected with the operation statistics module, the inrush current sensing module, the voltage sensor, the current leakage sensing module and the temperature collection module. The device provided by the invention collects the total number of operation times of the SPD, the inrush current of the SPD, the loading voltage of the SPD, the leaked current of the SPD and the surface temperature through the operation statistics module, the inrush current sensing module, the voltage sensor, the current leakage sensing module and the temperature collection module, thereby achieving the comprehensive collection of all parameters of the SPD, and laying a foundation for the estimate prejudgment of the SPD. According to the current and voltage values collected by the inrush current sensing module and the voltage sensor, the device calculates the actual impedance of the SPD, and prejudges the electrical performances of the SPD through comparing the actual impedance with a preset impedance threshold value and combining the comparison results with the leaked current of the SPD.