In order to investigate the multiphysics in the recoil process of magnetorheological damper, independent three-stage magnetorheological damper of double rod has been designed. The magnetorheological gel with carbonyl iron powder mass fraction of 70% (MRG-70) has been prepared and the steady-state shear test was carried out for obtaining the consistency coefficient k and the non-Newtonian index n of the Herschel–Bulkley model. MRG-70 has been applied to the damper and the motion analysis of the recoil part has been carried out by combining the law of chancing of the bore resultant force of a certain type of fixed artillery. Results of the theoretical analysis and numerical calculation of multiple physical fields for damper showed: (1) there was a scattered magnetic flux inside the damper. The magnetic field was generated by the combined coil with a high degree of nonlinearity and time variability; (2) the internal energy dissipation of damper comprises five parts, in which Poiseuille pressure flow loss and Couette viscous flow loss were the primary and controllable part of the damper. The temperature of each pole reaches a peak value, and it is different at different times; the pressure drop at the magnetic pole was less than the pressure drop at the coil; (3) the dynamic viscosity of the central axial surface of the effective damping channel shows obvious nonlinearity and time variability from the spatial and time dimension, and varies very sharply at each pole, and the peak value fluctuates with the position.