The invention discloses a power conversion unit of a static frequency converter, and a testing method. The frequency converter is connected into a 380-V low-voltage power supply under the working condition without a high-voltage power supply, and correctness of CT polarity, PT polarity, fiber loops and primary power loops can be verified through a single-tube trigger test and a full-bridge rectification test. According to the testing method, before a project is put into operation on site, under the situation that no high-voltage power supply is accessed for debugging, by externally connectingthe low-voltage power supply, the power conversion unit is effectively tested and verified, reliable operation of a whole system under the dynamic debugging mode is ensured, and testing requirements of a network bridge and a machine bridge of the frequency converter can be met simultaneously through two methods.