Abstract: In recent years,accidents of protection misoperation caused by multi-point grounding of the secondary winding of voltage transformer（TV） have occurred many times in power grid,resulting in serious economic losses.In order to prevent similar accidents,the on-line monitoring device for TV secondary N600 grounding and TV secondary intelligent grounding protector are studied and developed based on an analysis of TV secondary N600 circuit status.Therefore,the multi-point grounding intelligent monitoring system of TV secondary N600 circuit is constructed.And a complete set of methods and effective solutions of multi-point grounding monitoring and quick investigation for N600 circuit in substations are formed.