In order to solve the problem of rust prevention in brake disc process, a kind of non-trace water-based rust inhibitor for brake disc was prepared by using monoethanolamine, 21-C ternary fatty acid and binary organic phosphoric acid. Based on the electrochemical analysis, QB / T 2117-95, JB/T 9181-2016 and the application tests in the brake disc production line, the traceless water-based cleaner was characterized and tested. Results showed that the antirust agent had strong antirust property. When the concentration was 1%, the standards could be met. The best adding concentration was 1%～2%, which could be used in the pretreatment production line with phosphating process.