This paper presents the design of a multi-channel distributed monitoring platform, which is highly suitable to be applied into a traction supply system for urban railway transportation. In our platform are combined the technologies of Ethernet and virtual instrument, fully exerting their merits of large data capacity, high efficiency and low cost. With a HMI (Human Machine Interface) and a VO (Virtual Oscilloscope) in the platform, all the real-time data from traction supply system are presented to operators in a substation or control center. In the platform, there is a special Ethernet management software, realizing the protocols for Ethernet collision elimination, new IP allocation, and network health detection, and it has been proven to be practical and effective through field applications. There is also a DLL for the management of data among Ethernet, HMI and VO. Our HMI is developed with LabView, and the VO and DLL are with VC++6.0. The platform is subjected to the experiments on a prototype of novel traction supply system, and the experimental results are presented in the last part.