The invention discloses an oxytropis ehrig fungus alternaria FEL4-OOc which is preserved in the China type culture collection center on October 8, 2008, and the preservation code is CCTCC NO: M 208143. Bacterial colony of bacterial strain is in a circular shape with regular edges, the bacterial colony is white during early culturing period and gradually changes to gray, celadon and black as the culturing time is prolonged, and the centre of the bacterial colony slightly protrudes. Mycelium has transverse septa but has no mediastinums, and is relatively dense. Conidiophores peduncles grow on Part of the aging hypha, and the conidiophores peduncles have braches. The conidiophores are less in amount and brown in color, and are singly distributed in a scattered mode. The conidiophores have the2-5 transverse septa with thicker transverse septa films but have no mediastinums, ; spores are in long rod shapes and column shapes with the size of 30 to 90 microns*5 to 10 microns. The bacterial strain is obtained from leaves, stems, flowers or seeds of yellowflower crazyweed herbs through manual separation and filtration, and has the function of synthesizing main toxin, i.e. spherosin of the yellowflower crazyweed herbs.