This work presents an experimental investigation on the behavior of magnetorheological (MR) fluids in squeeze mode and a theoretical analysis of its MR mechanism. Relative to the well-known large normal stress in squeeze mode, the exciting velocity-dependent characteristics and the normal stress variation tendency of MR fluids are emphasized. The characteristics of MR fluids are tested under displacement-control and force-control modes. It is shown from the tests that along with the exciting velocity, the tensile stress shows an increasing tendency before saturation, but the compressive stress exhibits a decreasing tendency. In addition, under force-control mode (10 N/s) test, after the initial elastic deformation the elastic-plastic deformation occurs instead of plastic flow. As a consequence, in order to fully understand the exciting velocity-dependent characteristics of MR fluids in squeeze mode, a new concept considering both the hydrodynamic interaction between the particles and continuous phase and the magnetic field interaction among particles is proposed and discussed. Two separate models for the hydrodynamic interaction and magnetic field interaction in valve mode are derived by applying Darcy filtration law and simplified dipole model, respectively. It is demonstrated from the simulation and discussion that MR mechanism in valve or squeeze mode is developed on the basis of the balance between the magnetic field and hydrodynamic interactions, in which the hydraulic force is the main power propelling the deformation of the chains, and meanwhile, the restoring force resulting from the deformation of the chains makes the reaction on the relative motion. As a result, a macroscopic exciting velocity-dependent characteristic of MR fluids is presented showing the damping force of MR damper. (C) 2017 The Society of Rheology.