A simplified dynamics model of the whole aeroengine is established，based on a realistic aeroengine vibration testing rig. Hertzian contact theory is applied to model inter-shaft bearing. Used the Newmark-β/Newton-Raphoson method to solve the equation，the nonlinear response of dual rotor and casing of aeroengine are analyzed respectively. The effect of bearing clearance on nonlinear characteristic of the whole aeroengine is studied particularly. The result shows that phenomena like vibration jump，bistable state and the reduction of coupling degree between low- and high-pressure rotor are appeared with bearing clearance increasing. The casing can reflect the vibration characteristics of the rotor，but the situations of the measuring points at different positions of the casing are different. In general，the nonlinear vibration characteristics can be observed at the middle and rear measuring points when the corresponding phenomena of the rotor occurred. The research results are helpful to understand the influence of the nonlinearity of the inter-shaft bearing on the nonlinear vibration characteristics of the aeroengine system，especially the casing，and can provide certain guidance for the selection of the position of the measuring point on the casing of the aeroengine.