The cathodic pressure drop is an effective indicator for detecting the water state in flow channels and gas diffusion layer of the proton exchange membrane fuel cell. Reducing current density is supposed to be the easiest way to cure the fuel cell from flooding. However, the relationship among pressure drop, current density and flooding has not been investigated, which is meaningful for preventing flooding, especially for the stationary power plant featuring constant condition and long-time operation. In this paper, the evolution of pressure drop, voltage, impedance, and water amount in terms of the resistance at different parts inside the fuel cell were analyzed quantitatively using a new equivalent circuit model, which could describe the water state more appropriately under large water amount. For one thing, when the flooding risk was diagnosed at different current densities, the cathodic resistance of catalyst layer was almost 238 m Omega.cm(2), and the mass transfer resistance of the cathodic channels and gas diffusion layer was between 220 and 234 m Omega.cm(2). It implied that pressure drop could be used to detect flooding. For another, the pressure drop could not return to the control line, but the more the current density decreased, the closer it approached to this line, which was verified by the impedance at different layers. In real application, the appropriate strategy of lowering current and diagnosis based on pressure drop could be selected for avoiding flooding in advance.