Based on the fungal growth model, the authors develop an environmentally-adaptive parametric L-system and present a fractal image generation algorithm in this paper. This algorithm not only uses biological understanding of the flow of nutrients through the fungus to control the growth, but also takes the influence of the environment which fungus grow in into full account. The images generated by this algorithm have natural branching structure. By setting the environmental factor, its global-shape feature can be easily controlled. It is especially suitable for industrial pattern design, animation image design and so on.