In this paper, we present an interactive system for quickly and easily modeling 3D trees with ball B- spline curves(BBSCs). As BBSCs are flexible for modifying, deforming and editing, these methods provide intuitive interaction and more freedom for users to model trees interactively. These interactive methods can also be used in conjunction with other methods like generating tree models through L- systems or iterated function systems (1FS) so that the models are more realistic and natural through modifying and editing interactively. The system generates a 3D geometry as well as its topological structures through interaction.