The polarization characteristic (V-I curve) describes the basic working performance of proton exchange membrane (PEM) fuel cell. The variations of internal parameters including physical and empirical ones have great impact on the polarization characteristic. This paper investigates the parametric variations effect on the fuel cell voltage during the full range current. Some important parameters in the electrochemical domain and fluidic domain are selected and their influences on the mass transfer and electrochemical reaction are studied. The analytic results show that the positive- and negative-deviations of the selected parameters have very different effect on the cell voltage. Multi-parameter sensitivity analysis (MPSA) based on Monte-Carlo method is used to identify the sensitivity index of each parameter. The study results could provide a guidance for the parameter identification during the fuel cell modeling or manufacturing. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.