In order to realize the geometric modeling of plant flowers of crown united, taking tobacco flower as an example, a flower modeling method based on ball B-spline curve and parametric surface was proposed. Morphological characters were analyzed. Firstly, 3-D shape of each parts with mathematics were described and the control parameters were get. And then, visualization of them with relative color and topology information were realized. The results showed that proposed method could effectively simulate tobacco flower with good controllability. The models showed more reality, which provided a new technique for explicit modeling of other similar flowers.