It is important to study on the quantification of plant development when constructing virtual plant model based on the rules of botany. Considering a plant as a constructive system, the changes of topological structure and organisms, such as internode and leaf of plant, were quantitatively analyzed by means of the morphology and physiology of botany. A method for constructing a virtual plant model was also proposed in this work. The simulation results of a plant growth process by this model demonstrates the feasibility and validity of the model.