The invention provides a lightning overvoltage measuring system, which comprises a lightning overvoltage sensor, a high-speed data acquiring and processing unit and a solar power supply system, wherein the lightning overvoltage sensor is realized by adopting a high-speed capacitive voltage divider, and can be used for acquiring instantaneous voltage during lightning overvoltage through the operation of the high-speed capacitive voltage divider; the high-speed data acquiring and processing unit is used for acquiring a low-voltage signal from the lightning overvoltage sensor; the low-voltage signal is firstly subjected to analog-digital conversion through an analog-digital converter, and is buffered in a buffer; a processor is used for reading data in the buffer for processing. The solar power supply system can be used for providing energy for the lightning overvoltage measuring system without connecting a general alternating-current power grid power supply, and the influence of measuring high voltage generated by lightning on an alternating-current power grid is avoided.