The aim of this study is to understand and explore the rheology of

dense granular flow, in particular the phenomenon of regime

transition, using both microscale DEM (discrete element method)

simulations and macroscale modeling methods. The rheology of dense sheared granular flow in a Couette device is simulated using DEM. It is found that DEM simulations are capable of capturing the regime transition from quasi-static to intermediate behavior. A constitutive model based on the order parameter (OP) framework is refined, and a linear model with new model coefficients extracted from data of 3D DEM simulations of homogeneously sheared granular flows is proposed. The performance of different constitutive models including the refined OP model is tested in the intermediate regime of granular flows. None of these models captures the correct scaling of shear stress with shear rate in the intermediate regime, leading to the conclusion that further development of constitutive models is needed for dense granular flow in the intermediate regime.