Insulation resistance detection system and method of direct current system

The invention provides an insulation resistance detection system and method of a direct current system. The detection system comprises a first insulation monitor and a second insulation monitor which are in communication connection. The first insulation monitor comprises a first detection bridge J1, a second detection bridge J2 and a first balance bridge P1 which are connected between the positive electrode of the first bus and the negative electrode of the first bus; the second insulation monitor comprises a third detection bridge J3, a fourth detection bridge J4 and a second balance bridge P2 which are connected between the positive electrode of the second bus and the negative electrode of the second bus; the first insulation monitor is an insulation host, or the second insulation monitor is an insulation host; and the insulation host realizes time-sharing detection of the positive pole to ground impedance and the negative pole to ground impedance of the first bus and the positive pole to ground impedance a