Our country traditional method for the autopassing phasesplitter device of electrical locomotive is manual detection, this method exists some shortcomings of low efficiency, no scientific test, less amount of data, great influenced by artificial factors, unable to be scientific and systematic analysis. In order to solve this problem, studying a online state inspecting system for the autopassing phasesplitter automatic device, is of great practical significance. By simulating the working state of locomotive passing the phase splitter, detecting the changing process of orbital current, judge whether the autopassing phasesplitter device can work normally. This paper expounds the working principle of the detection system in detail, introduces the overall architecture of the system, the functions, the features and the results of the system are analyzed.