Abstract: In this paper, a new method for measuring and computing the leaf area of leaf trees by means of function interpolation and numerical integration is presented. The counted results bear out that this method is easy to apply and has higher accuracy. Computations show that each parameter of the leafblade is somewhat related to the leaf area but the most important one is the product of the leaf-width and leaf-longth. Some regression equations for counting the leaf area of common leaf trees in South China are also incorporated.