The electric compound turbocharger(ECT) which integrates a high speed motor into a turbocharger rotor shaft can be used transiently to accelerate the turbocharger more quickly in response to an acceleration requirement. It can utilize the exhaust gas energy fully to improve the engine fuel efficiency and benefit for engine with lower emissions. The key technique of ECT is to solve the reliability problems when an electrical motor is integrated into a turbocharger shaft between the turbine and compressor wheels will increase the burden for the bearing support and affect the turbocharger shaft rotation characteristics. In order to know the dynamics behavior of higher load bearing system is explored for reliability, this paper focus on the nonlinear rotor dynamics characteristics of ECT rotor bearing system. Based on the principle and structure of ECT rotor bearing system, the basic theory method and dynamics model of rotor bearing system is established considered the nonlinear fluid film force. The shaft critical speed, unbalance response, stability performance are analyzed, the nonlinear film whirl and the film oscillation analysis show a complex rotor dynamic behavior of ECT. The influence on the key structural parameters and film clearance for rotor bearing system are discussed. The nonlinear rotor vibration characteristics of electric compound turbocharger under actual operating conditions are predicted. The results can support a theoretical basis for the design of nonlinear shafting dynamics of ECT and increase rotor bearing system reliability for future products.