Abstract: The essential oil was extracted by hydrodistillation from the leaves and inflorescences of Solidago canadensis L. The orthogonal experiment of L9(34) were used to optimize the extraction of essential oil,including influences of solid-liquid ratio,immersion time and distillation time. The antifungal ability of flowers and leaves' essential oil on B. cinerea were investigated by contacting method,and then the changes of mycelial were observed by scanning electron microscope(SEM) and transmission electron microscope(TEM). The results showed that immersion time was the most influential factor,and the optimal extraction method was that solidliquid ratio was 1∶12(g/m L),immersion time was 3h and distillation time was 3h. The essential oil from two parts of the plant showed a good antifungal activity on B. cinerea. The treated hyphae became to be shrinking and much thinner than the controlled,the structure of cell wall was damaged and became to be loose. The subcellular structure and its membrane dimmed and disappeared,the cytoplasm exosmosis increased. The essential oil from leaves of S. canadensis showed higher antifungal and damage ability than that of flowers.