In this paper, a substrate utilization function is designed to simu-late the functioning of the enzyme system which manipulates the par-titioning of substrate in rice bodies. According to the carbon balancerule and the Michaelis-Menten law, a group of numerical simulationmodels, which can be used to quantitatively describe the relationshipbetween weather factors and the vegetative growth and yield formationof rice crop, are set up.