The present invention provides an overvoltage protective device used for a natural gas pipeline system. The natural gas pipeline system comprises a natural gas pipeline and a cathode protection device, and the cathode protection device is connected with the natural gas pipeline through a first wire. The overvoltage protective device comprises a first switch arranged on the first wire; a grounding device connected with the natural gas pipeline through a second wire; a second switch arranged on the second wire; a voltage measuring device connected at two ends of the second switch; and a control device for comparing the voltage measured by the voltage measuring device with a pre-set action voltage and controlling actions of the first switch and the second switch according to the comparing result. With adoption of the overvoltage protective device provided by the present invention, a pipe-ground potential difference of the pipeline at a valve chest is limited within a safe value, thereby guaranteeing personal safety and valve chest equipment operation security, and avoiding the problem of electrochemical corrosion aggravation caused by inflow and outflow of stray current after long-time earthing of the pipeline.