Abstract: Vacuum interrupter has been used for more than 50 years in power system, and its occupancy has exceeded 90% in middle voltage occasions. The online detection for vacuum degree has been investigated for more than half a century as well, whereas, no good-performed online detection method can be applied to practical applications. The vacuum degree detection of vacuum interrupter during last 50 years is reviewed in this paper. The service conditions and failure statistics of vacuum interrupter are summarized. This paper emphasizes the principles, challenges, merits and demerits of the existed vacuum degree detection methods of vacuum interrupter. As vacuum interrupters trend to develop from higher and lower voltage fields, a method with high sensitivity and precision is highly demanded to overcome the predicament of observation method, which is used in online detection. Based on the current research status, the implantation of miniature, high-temperature-resistant gas sensors in the vacuum switch or the use of non-contact optical measurement methods will be expected to realize the charging or online detection of the vacuum degree.