A method with non-grounded neutral point is widely used in the power system of mine,the fault line via on-line insulation monitoring system can be found out.On the basis of analyzing problems existed in the existing leakage protective equipment,the simulation research of insulation parameter on-line monitoring for mine low voltage cable with additional low frequency signaling based on Matlab simulation technology is adopted and the principle and implementation method of insulation parameter on-line monitoring function are introduced.Elective earth leakage protection can be realized.