The invention discloses a measurement system for a lightning electric field changing signal and a measurement method thereof. The digital measurement system at least comprises a planar antenna, an electric field analog-to-digital conversion module and a digital signal processing module. The input end of electric field analog-to-digital conversion module is connected with the planar antenna, and the outer end is connected with the digital signal processing module. The planar antenna is used for detecting an electric field changing signal which is generated by the lightning and transmits the electric field changing signal to the electric field analog-to-digital conversion module. The electric field analog-to-digital conversion module is used for processing and converting the electric field changing signal, obtaining the digital lightning electric field changing signal and transmitting to the digital signal processing module. The digital signal processing module is used for triggering acquisition and processing the digital lightning electric field changing signal for obtaining a lightning electric field quick-changing signal, a lightning electric field slow-changing signal and a lightning electric field original signal. Furthermore the digital signal processing module stores the signals and combines for forming data frames for communication with outside. The measurement system and the measurement method realize measurement for quick change and slow change of the lightning in a low-cost and high-efficiency manner.