In order to describe the change of the failure rate of computerized numerical control（CNC） machine tool motion components with time，this paper starts from the meta-action unit and proposes a new meta-action unit failure probability model. First，according to the cause of the meta-action unit failure，the failure types are divided into two categories：random failure and aging failure. Then，according to the different characteristics of the failure data of these two failure types，two different probability distribution functions are used to describe separately，where random failures are described by Poisson distribution，and aging failures are described by Weibull distribution. Next，the physical meaning and estimation method of each parameter in this failure probability model are given. Furthermore，the working load and working environment respectively affect the failure rate of the aging failure and random failure of the meta-action unit. In order to compare the magnitude of their influence on the failure rate，the working load parameter Rl and the working environment parameter Re are proposed，and the estimation method of the two parameters is also given. Finally，according to the collected failure data of the moving components，a frequency distribution histogram is made. At the same time，the probability density function is obtained by parameter estimation of the failure data，and these two are drawn on the same graph. It is found that both have a better simulation effect. The simulation effect shows that the proposed failure probability model of the meta-action unit is suitable for describing the change of the failure rate of moving components with time，and thus the model is effective.