Abstract: Currently,electrochemical impedance spectroscopy is widely used for fault diagnosis of fuel cells. In view of the high cost of diagnostic equipment,an EIS test method integrated in the DC/DC converter of the fuel cells system is proposed. An excitation signal is applied to the reference signals for dual-loop control of the converter separately. It causes broadband online disturbances of fuel cells’ current and voltage. For faster testing,a kind of pseudo-random binary sequence is designed as the excitation signal to meet the needs of bandwidth and power intensity. The experiment uses MATLAB/Simulink for modeling and simulation,and is verified by hardware-in-theloop experiments. This method meets the requirements of time consumption and high accuracy,and online testing can be realized through embedded systems.