In actual production, the rotor winding state monitoring of doublyfed induction generator (DFIG) could effectively improve the operation reliability of wind turbine. The complete experimental program for research on rotor winding fault of DFIG was provided. Firstly, the basic principle and field experimental devices of the experimental platform, as well as the solutions to problems in the process of platform building were introduced so as to ensure the accuracy of experimental data. Then, taking the converter side current as the research object, we analyzed the propagation of fault information through the power converter electronic device, and extracted the diagnostic characteristics of rotor winding unbalance fault based on current spectrum. Finally, the current spectra of rotor windings before and after the unbalance fault caused by threephase unbalance loads were obtained by experiments, and, in combination with the theory of electrical fault characteristic frequency on the rotor side, the fault characteristic frequencies were analyzed. According to the experimental results, 100 Hz, 200 Hz and several characteristic frequency components of rotor converter side current spectrum were selected as the diagnostic characteristics of the rotor winding unbalance fault. It was significant to take 3sf and (2±3s)f (s: slip ratio;f: fundamental frequency) as the characteristic frequencies of rotor threephase unbalance load fault in engineering and experiments.