The invention relates to the technical field of cable equipment detection, in particular to a partial discharge on-line monitoring and diagnosis method, which comprises the following steps: step 1, data acquisition, step 2, monitoring system establishment, step 3, detection and diagnosis, step 4, risk classification, step 5, risk tracking and step 6, risk control. According to the invention, through an electromagnetic field sensing module, a noise sensing module, a temperature sensing module, a humidity sensing module and a dust sensing module, the surrounding environment can be conveniently detected, the equipment can be conveniently protected in advance according to the measured data, and the influence of the environment on a discharge signal can be conveniently analyzed; and the accuracy of discharge signal detection is improved by recording the surrounding environment and conveniently comparing the recorded surrounding electromagnetic data, the discharge diagnosis result is more intuitively compared through the discharge accumulation comparison diagram and the similar characteristic pulse comparison diagram, the high-voltage cable edge defect condition is judged, and the detection and diagnosis effect is improved.