The utility model discloses an online monitor device for the service life of an arrester with gaps, which is composed of a sampling energy acquisition module, a high current trigger counting circuit module and a low current trigger counting circuit module all interconnected in series on an grounded wire of the arrester, wherein the sampling energy acquisition module is respectively connected with a first rectifier bridge in the high current trigger counting circuit module and a second rectifier bridge in the low current trigger counting circuit module through a first side coil and a second side coil which are output respectively, the high current trigger counting circuit module is internally provided with a first capacitor which is connected with a high current trigger counter via a threshold voltage control circuit, and a direct current terminal of the second rectifier bridge in the low current trigger counting circuit module is connected with a second capacitor and a low current trigger counter in parallel. The online monitor device of the utility model, as a passive component, is simple in structure, long in service life, strong in visibility and suitable for recording total times of lightening strike of metal oxide arrester with gaps of 35kV or more and for monitoring the predicative service life of arrester online.