The invention discloses an online electric abrasion detecting method and system of a vacuum circuit breaker. The online electric abrasion detecting system comprises three current transformers, a current signal conditioning unit, a digital-to-analogue conversion unit, three electric arc property probers, an electric arc signal conditioning unit, an arc time pre-treatment unit, an on-off frequency counting pre-treatment unit, a central processing unit, a local alarming unit and a power supply unit. By improving the forecasting and the selection of an online detection actual parameter of electric service life in an on-off current weighting accumulation method, the influence caused by a wider parameter selection range in an estimation and calculation process according to experience data, particularly large result deviation caused by single abrasion amount accumulation by an on-off current index, can be overcome.