Abstract: A magneto-rheological (MR) recoil damper for a 25 mm air defence gun test application is studied. Based on Herschel-Bulkley shear model, a one-dimensional axisymmetric laminar flow model of the MR recoil damper is proposed, and the relation curves of damping force and piston velocity of the MR damper are obtained according to the proposed model. Using the force-velocity characteristics of the MR damper, the recoil dynamic equation of the 25 mm gun is solved, and the recoil velocity and recoil displacement of the gun are obtained. The simulation results indicate that the value of the MR fluid behavior index has a very big influence on performance of the gun magneto-rheological (MR) recoil damper.