In practical engineering, the fault of brush slip ring of Doubly-Fed Induction Generator (DFIG) occurs frequently, and the excitation stability of the motor is also greatly affected, which will lead to the disconnection of the generator set. Therefore, this paper proposes a fault diagnosis method of burn of doubly-fed induction generator brush slip ring based on Hilbert Huang Transform (HHT). First it uses the PSCAD/EMTDC power system simulation software to simulate the slip ring burn fault and obtain excitation current through the brush and slip ring before and after fault. Then fault features are extracted based on HHT theory, and the simulation results and the Hilbert spectra gotten from the measured excitation current signal are compared and analyzed to verify the feasibility of fault feature diagnosis method. Finally, the concept of energy quotient diagnostic features is proposed, the energy quotient of features of different fault levels calculated and then compared with the slip ring surface temperature value measured by the infrared temperature measuring probe. Their variation trend is analyzed, finding that the periodic frequency the components which is higher than 100 Hz can be used as the fault feature, and its energy quotient has higher accuracy and sensitivity in diagnosing minor burn of slip ring. This method provides some guiding significance for practical engineering research. This work is supported by National Natural Science Foundation of China (No.51177039 and No.51577050).