The invention relates to a direct current insulation monitoring device. The device comprises an intelligent adjusting circuit, and the intelligent adjusting circuit comprises a controlled current source and a switching device used for connecting the controlled current source between a positive bus-bar and the ground or between a negative bus-bar and the ground. The vector sum of current flowing through balance bridge resistors to the ground is detected in real time, if the vector sum of the current is plus, the controlled current source is connected with the positive bus-bar, if the vector sum of the current is minus, the controlled current source is connected with the negative bus-bar, and then the voltage, to the ground, of the positive bus-bar and the negative bus-bar is adjusted. In this way, it is prevented that when an unbalanced bridge is switched, the fluctuations of the voltage, to the ground, of the positive bus-bar and the negative bus-bar of the insulation monitoring device cause false action of an exit relay.