This work proposes a modified Bingham model for describing magneto-rheological fluid (MRF) damping force by experimental data. The model parameters have direct physical significance to the MRF damper properties. In addition, the primary resonance reduction in a single-degree-of-freedom (SDOF) skyhook controlled system is investigated. An analytical solution for the system’s primary resonance is obtained, which is verified by numerical solution. The effect of changing physical model parameters on the system’s primary resonance is also studied.