In order to detect the insulating property between the spacecraft thermal test external heat flux simulator and spacecraft, the heating cable insulation resistance automatic test technology is studied. a heating cable insulation resistance test system based on PXI bus is developed. The input channel switch device of heat cable is designed through relay matrix technology, the cable multiple core channel scanning and the insulation resistance measurement is reached through PXI bus technology，ant the control software is developed through VC++6.0. The test result shows that the system can detect the insulation fault of eight heating cables quickly and reliably, and greatly improve the automatic level of spacecraft thermal test.