Abstract: Fault diagnosis and its tolerant control online of the clutch actuator motor quickly and effectively is the precondition to ensure safe and reliable operation of dry dual clutch transmission(DDCT) and to accomplish its power shift. Dual Kalman filter is used to jointly estimate the states and parameters of clutch brushless DC actuator motor of six-speed DDCT. And the feasibility of estimation algorithm is verified by bench test. Results show that the proposed joint estimation algorithm can estimate the states and parameters of the clutch actuator motor effectively with the relative error no more than 2%, and the proposed algorithm can furtherly diagnose the potential fault of the motor in real time which can't be found through sensor signals. The study lays a foundation for the subsequent fault tolerant control of the DDCT.