We investigate the dense-flow rheology of granular materials with various size distributions through discrete element simulations of simple shear flows of frictional, spherical particles with binary, linear, Gaussian, and lognormal distributions in size. Dense shear flows of monodisperse granular materials exhibit three regimes: quasistatic, inertial, and intermediate. It is found that these regimes persist for polydisperse granular materials as well. However, the critical volume fraction that separates the quasistatic and inertial regimes is found to increase when particles manifest size distribution. This increase in the critical volume fraction can be described with fair accuracy by polydispersity and skewness alone regardless of types of distributions. Furthermore, the inertial number model for stress ratio is found valid for particles with size distribution. A rheological model is proposed that captures the simulation results on stresses for all the size distributions studied.