Inter-turn short circuit is a common fault in reactor. In view of the current situation of insufficient condition based maintenance of reactor, an on-line monitoring method suitable for Inter-turn short circuit fault of distribution reactor was proposed in this paper. Firstly, the equivalent circuit model of reactor was built, and the calculation method of electrical parameters of reactor was obtained; Then, a set of on-line monitoring system for reactor short-circuit fault was built. Finally, the short-circuit test of reactor under different fault location and fault degree was carried out. The results show that the equivalent reactance and resistance change rate of inter-turn short circuit of reactor have the symmetry of short circuit position, the absolute value of change rate in the middle is the largest, and the absolute value of change rate at both ends is the smallest. With the deepening of short-circuit fault, the equivalent reactance decreases and the decreasing range increases. The equivalent resistance shows an increasing trend, and the increasing range increases. This research technology can realize the effective monitoring of inter-turn short circuit fault of distribution reactor.