According to the solar-blind characteristic of the pantograph arc spectrum distribution, an arc detection method based on the photoelectric conversion mechanism for urban rail was proposed, and the design of each part of the arcing detection system was completed. Through the analysis of arc spectral distribution, the 275-285 nm band was determined as the detection characteristic waveband. The optical acquisition system located on the roof of the train collects the arc characteristic light and transmits it to the photoelectric conversion module, which converts the received optical signal into the corresponding current signal linearly. After amplification, comparison and screening in this module, the optical signal is sent to the data processing module for output display. Finally, a field test conducted on an urban rail transit line shows that this arc detection system can effectively detect the pantograph arc phenomenon and reflect the arc intensity linearly avoiding the influence from natural light, train load and train running direction.