The invention discloses a three-dimensional digital tree growth modeling method based on joint constraining of illumination and growth equations, so that a technical problem that the existing three-dimensional digital tree growth modeling method can not constrain the growth height of the tree is solved. The method disclosed by the invention is characterized in that according to a plant growth equation, ring-to-ring iterative growth is carried out by inputting a starting position and an initial trunk direction of a three-dimensional digital tree root as well as illumination information of the tree growth space. Illumination resources obtained by terminal buds and lateral buds of all branches are calculated; convergence and allocation volumes of the illumination resources are calculated; growth speeds of the trees are constrained based on a growth equation and whether each terminal bud and each lateral bud grow are determined and the growth speeds are determined; and new branch positions and geometric values of branch models are calculated and radius values of all nodes of the branches are updated. And after iterative growth stopping, a branch model is outputted and leaves are added. Therefore, a technical problem that the growth height of the tree can not be constrained on the condition of full illumination resources is solved.