Rotor-Active Magnetic Bearings (rotor-AMBs) systems nowadays have been widely used in turbomachinery where different methods for assembly were used such as impeller mounted using shrink-fit. In our experiments we noticed that the conditions of shrink-ft assembly can introduce instabilities on the levitated rotor at rest. To understand and give recommendations (on the assembly conditions), a numerical model was developed and then was validated experimentally. The effect of the shrink-fit interface contact was modelled as a contact force acting on the rotorAMBs system introduced by distributed spring units with a given contact stiffness. Considering that there was partial separation in the contact interface due to the AMBs levitating forces, a novel contact force model related to contact status was established by calculating the real-time contact area. A microscopic contact model based on fractal theory was developed to calculate the contact stiffness. The model developed was then validated experimentally simulating the levitating rotor at rest. The rotor response was analyzed in frequency domains by applying the different conditions of shrink-fit interference and contact length. The shrink-fit contact conditions influenced the system stability and made the fourth bending mode unstable. The increase of shrink-fit interference and contact length decreased closed-loop system stability and increased the amplitude of the rotor vibration response. The model reliability was assessed and a stable region using combinations of shrink-fit parameters on the assembly conditions based on the results of stability analysis was established.