With the continuous improvement of the quality requirements of MMC-HVDC transmission system, the detection of the power module of its core components will be more comprehensive. The traditional power module test device can not measure the capacitance and voltage resistance of the power module separately, resulting in its failure to locate the fault, and the aging condition can not be monitored which makes the power module of MMC-HVDC potentially dangerous. In order to effectively improve the defects of the current power module test device, this paper presents a method of using the least square algorithm to realize the high-precision and fast measurement of the resistance and capacitance of the power module. This method improves the measurement accuracy step by step through the input of multi-stage least square method. The multiple accuracies are verified by the engineering power module which makes the method be able to monitor and quickly screen the health status of the power module capacitors and voltage equalizing resistors on the project site, effectively avoides the potential hazards of the power modules of the straight line project, and fills the gap of high precision and fast resistance capacitance calculation of the flexible and direct engineering testing device.