A comprehensive Distribution of Relaxation Times (DRT) analysis is carried out for a proton exchange membrane fuel cell (PEMFC) in this research, to achieve stack-level fault diagnosis by Electrochemical Impedance Spectroscopy (EIS). The durability and reliability of PEMFC are still crucial challenges for its commercialization, and EIS is a potential characteristic tool for diagnosis. However, the explanation and application of EIS are still ambiguous and insufficiently exploited for the PEMFC stack. DRT is a useful tool for EIS analysis, but it has not been applied to stack-level PEMFC diagnosis yet. In this work, to explore the possibility of using DRT as a PEMFC diagnosis tool, experiments are designed and carried out under different operating conditions, while the current, stoichiometry of the cathode, stoichiometry of the anode, temperature, and relative humidity are adjusted. Further, the detailed method to analyze PEMFC EIS data by DRT is presented, and the relationship between the PEMFC fault and DRT is built according to massive experiments and quantitative analysis. The DRT peaks can be assigned to the corresponding inner processes, and the diagnostic significance of the DRT features is quantitatively compared. Additionally, a novel equivalent circuit model (ECM) structure is proposed according to the DRT analysis, which is composed of 6 resistor-capacitor circuits that correspond to the inside processes, thus significantly contributing to stack-level fault diagnosis.