Surface desquamation is the major performance of the NC machine tool malfunction. The malfunction can be diagnosed through whether running character frequency and its harmonic wave of the bearing inner ring or outer ring is present in the shock vibration produced by the malfunction. This article establishes a dynamic model of surface desquamation, a bearing vibration state model and observation model. Meanwhile the vector of the model is obtained. It has been proved through emulation and experiments that bearing malfunction signal can be effectively traced and estimated by Kalman filtration.