The description of plants appearance in nature is a hot topic in modern times. If save a plant graphics information in the form of a picture, the fineness of graphics depends on the storage format of the image and the amount of space it takes up. And it’s very difficult to realize the change to the graphics as a whole. By utilizing the computer language to model plant morphology can calculate and get plant graphics with only dozens of numerical, and it is easy to modify the whole graph. In the field of plant appearance modeling, fractal geometry can use the self-similarity of graphs to describe the natural appearance of plants better. Chaos theory, which is nonlinear as same as fractal geometry, also plays an important role in the description of natural objects. To improve the precision of object rendering, this paper proposed a plant morphology modeling algorithm based on theory of the fractal geometry and chaos. The uncertainty of chaos is utilized to the operation of fractal geometry. The probabilities of entering a periodic orbit are set. And then the system does the calculations based on the periodic orbitals that come in. A basic tree graph is drawn by this algorithm, and the thickness of tree trunk, the height of branch and density of tree are adjusted by adjusting the parameters in the affine transformation matrix, which verifies the feasibility of the algorithm. The experimental results demonstrated that the graph of plant drawn by this algorithm is close to the real object in nature and the algorithm is suitable for describing the object in nature.