A kinetics model for the precipitation of M23C6 in high Cr ferritic heat resistant steel during tempering has been developed assuming the site-saturated nucleation, carbon diffusion-controlled growth and soft-impingement. The growth coefficient in this model is temperature-dependent, and the Arrhenius equation is applied to describe the growth coefficient, in which the growth activation energy is nearly equal to the diffusion activation energy of carbon in martensite. The effect of main parameters in this model has been discussed in detail. By this model, the precipitation of M23C6 during tempering can be predicted accurately in the case of 2D, and a good agreement with experimental data in previous work has been achieved. Copyright © Materials Research Society 2013.