Abstract: After seeds of Hellanthus annuus L. were treated by space flight, a mutant plant with flower characters was screened, and the traits of this plant was compared with normal plant. it was found that the petal got enlarged and elongated and the anther got small. But there was no change in the ovary and style. In the same floral disc, the petal of external was bigger than that of the internal. The microspore of the mutant plant was two times as big as the control. Compared to the control, the spermo-nucleus of mutant plant differentiated earlier, which was a good material to screen.