Abstract: The insulation of vacuum breaker, in which vacuum is adopted as insulating medium, depends on the vacuum degree of the vacuum interrupter. Although the history of vacuum breaker has more than 50 years, the vacuum degree online detection of vacuum breaker is still an international challenge, and existing means cannot be adopted to achieve reliable online monitoring. This paper proposes a vacuum detection method based on laser-induced plasma that multiplexes plasma optical path and laser optical path, and obtains the law of laser-induced plasma radiation intensity with vacuum degree at coaxial imaging. The experimental results show that the integral of plasma radiation intensity decreases monotonically with the degree of vacuum in the range of 10^-4 Pa~1 Pa, which can be used to characterize the degree of vacuum. The effects of delay time and laser energy on the performance of vacuum detection were studied, and better device design parameters were obtained. Furthermore, the stability of laser plasma is studied by laser plasma coaxial imaging, and the coefficient of variation of laser plasma radiation intensity at different pressures is calculated. The results show that the maximum coefficient of variation of laser plasma radiation intensity is 0.085 1, showing that laser plasma has good stability and repeatability.