Numerical simulation and experimental analysis for a magnetic circuit model of a damper were carried out by adjusting the size of the auxiliary gap to obtain greater magnetic field strength and wider adjustable multiples of the damping force. Results of experiment indicate that there is a specific ratio of sizes between the auxiliary gap and the working gap; this gap ratio is 3:1. The adjustable multiple and gap ratio is validated by the results of the experiment. The largest value for the magnetic induction in the working gap can reach 80–90% of the maximum; the least value is close to zero, and the adjustable multiple of the magnetic induction is near about a factor of 7. Experimental data also indicate that the law of the magnetic flux leakage is affected by the size of auxiliary gap as well as the intensity and direction of the current. Performance testing of the real optimal damper reveals that the maximum damping force of the damper is 195.7 kN, which is ~92.7 percent of the theoretical maximum value, at a gap ratio of 1:2.5.