The invention provides a cascade converter sub-module single-phase test circuit based on a symmetrical bridge arm structure. The cascade converter sub-module single-phase test circuit comprises a current generator and two groups of test bridge arms with the same structure, and the current generator provides a test current for the test bridge arms; the two groups of test bridge arms comprise a plurality of tested sub-modules which are connected in series, and the two groups of test bridge arms are in a reverse series connection structure. According to the invention, working condition simulationof a plurality of sub-modules of the cascaded converter in rectification and inversion operation modes can be achieved, simultaneous test of the plurality of sub-modules can be achieved, and the testefficiency is greatly improved. In addition, the structure of reverse series connection between the test bridge arms can counteract the direct current component in the capacitor voltage, and the power supply requirement of the current generator is reduced.