The visual interactive design of plant root system is significant to improve the whole research level of virtual plant growing research. The authors proposed an interactive precise design method to construct plant root system, taking corn root system as an example. First, the structure characteristics of corn root system was analyzed and its topological structure was established; then interactive framework model was used to construct the whole body structure; density function was designed to determine the number of branches and distribution; template technique was used to generate similar parts, and random L system with parameters was used to generate the first level lateral roots and root hair. After precise modeling of all the component parts of corn root system, all parts were integrated into intact root system. This approach integrated many visual design methods; the interaction and realism are very good. Using this approach, all the component parts of corn root system can be represented very well in detail, and the whole structure can be demonstrated very well. The research and design way of this system is quite popular and general, and it provides some valuable references for other similar plant visualization modeling.