The invention discloses a fault-tolerant control method and device for collaborative adaptive 
cruise control expected function safety, and the method comprises the steps: building an augmented 
state space model including 
radar sensor and control execution 
system performance defects which takes a 
radar sensor and a vehicle-mounted 
inertial measurement unit as feedback input, V2X collaborative information as feed-forward input, and takes a relative 
distance error, a relative speed and a self-
vehicle acceleration as output ; constructing a 
transfer parameter estimator, an augmented state estimator and a control execution performance defect estimator on the basis of the model, and estimating the augmented state and the performance defect of the 
cooperative adaptive cruise control system in real time; and comprehensively calculating an online 
active fault-tolerant control rate, inputting the online 
active fault-tolerant control rate into a vehicle 
chassis control system, and generating an accelerator pedal opening degree and a 
brake pedal opening degree. The situation 
cognition and scene adaptability of the 
cooperative adaptive cruise control function can be enhanced, so that the 
cooperative adaptive cruise control function can still operate safely and stably under the condition of multiple performance defects, and the expected function safety of the function is guaranteed.