GreenLab model is an on-going research program conducted jointly by researchers from France and China since 1998. It is oriented to be a functional-structural model for agronomy/forestry applications. Therefore, while keeping a property of being faithful to botanical knowledge, a new methodology is developed within GreenLab by stressing on simplicity of the model. This paper presents briefly our understanding towards plant functional-structural model, but only a model related to plant structures is given to show some progresses of the GreenLab. For a single stand of plant, GreenLab applies its newly developed "dual-scale automaton" approach to generate stochastic structures of plants. Using graph-based interface, this approach provides users with straightforward means of integrating botanical knowledge, i.e., metamers and growth unit, in construction of topological and morphological structures of plants. On the other hand, for a complex tree or a plantation application, a strategy of substructures is employ d in GreenLab model for fast construction of plants and calculation of yields in terms of organs. Simulation results indicate promising benefits in using the new methodology to develop a generic plant model in regard to the structural part. (Résumé d'auteur)