The invention relates to a lightning monitoring and early warning method and system. The method comprises the steps of S1, detecting atmosphere average electric fields, optical radiation signals, electric field changing signals, magnetic field changing signals and GPS satellite signals of an area to be monitored and conducting signal conditioning and conversion, S2, judging whether the electric field changing amount meets preset triggering conditions or not according to the electric field changing signals, conducting signal collection and storage and executing the step S3 if the electric field changing amount meets the preset triggering conditions, and refreshing and awaiting if the electric field changing amount does not meet the preset triggering conditions, S3, conducting waveform characteristic extraction on the collected optical radiation signals, the collected electric field changing signals and the collected magnetic field changing signals, conducting cloud-to-ground lightning identification and location according to extracted characteristic parameters, and meanwhile storing and displaying the position of lightning in a geographic information system, the lightning time and waveforms of the optical radiation signals, the electric field changing signals and the magnetic field changing signals in the lightning process, and S4, generating early warning results according to cloud-to-ground lightning identification and location results and atmosphere average electric field amplitudes, and giving an warning signal according to the early warning results.