The fast isolation switch is one of the key components of the hybrid DC circuit breaker, and its opening and closing time is within a few milliseconds, and the conventional circuit breaker is difficult to provide such a fast operating speed. Based on the experience of vacuum switch development, this paper analyzes the demand of DC fast isolation switch, and conducts a series of targeted tests on the application of vacuum small gap in DC isolation and arc-free breaking. At the same time, the problem of multi-fracture voltage balancing is solved by means of test and theoretical analysis. The medium voltage vacuum switch can be extended to the high voltage DC isolation switch application field. A 200 kV DC fast isolating switch with opening speed less than 3 ms is developed, and the scheme has the advantage of easy expansion to high voltage, which can meet the application requirements of hybrid DC circuit breaker.