Pellet fluidized bed reactors have been widely used to soften water. Reports from laboratory-scale research on the particle growth kinetics of calcium carbonate in pellet reactors have been put forward. However, the reports have not been comprehensive as they only consider the influence of supersaturation on the calcium carbonate growth process. The influence of three factors, namely, the superficial velocity (SV), particle size (L0), and supersaturation (S) on the particle growth rate of calcium carbonate were investigated in a pilot-scale study, and two models of particle growth rate and fixed bed height growth rate were built. The linear particle growth model G = 3.90 × 10−SV1.93L0−1.56S2.13 at the bottom of the pellet reactor was built based on a pilot-scale study of particle growth kinetics influenced by SV, L0, and S. The growth of the fixed bed height is closely related to the particle growth and also influenced by the three factors. The fixed bed growth model Rh = 5.19 × 10−8SV1.65L0−0.93S2.58 also incorporates SV, L0, and S, and provides a method for calculating the fixed bed height. The two models were built based on the pilot-scale experiment and were different from those previously reported. They are applicable as pellet discharge guides and are used in the management of pellet reactors.