The isolated single dangling bonds on the diamond growth surfaces are believed to be the active bond sites for the surface growth of diamond in chemical vapor deposition (CVD) systems. If more than one dangling bonds connect with each other at some areas of the surface, they may reconstruct and form π-chain or dimer bonds because of the higher partial surface energies at such areas. These π-chain or dimer bonds are the templates for graphite growth and can be restrained by the etching action of the active hydrogen atoms in the deposition atmosphere. Assuming that the occurrence probability of each dangling bond at any site of the surface is random, the probability functions of a bond site occupied by an isolated dangling bond or one of the dangling bonds in a dangling bond cluster have been worked out respectively. Then, the typical experimental curve of the CVD diamond growth rate can be reasonably explained. When the probability of a surface bond site occupied by an isolated single dangling bond is maximum, an optimum hydrogen coverage of 0.86 monolayer (ML) of the CVD (111) diamond surface can be achieved and this corresponds to the highest surface growth rate of diamond. This mechanism is proposed by us as a reduced diamond surface growth model.