Abstract: Screening of siderophore producing bacteria in the soil and factors influencing its secretion were studied. Results of two methods using selected-medium CAS(chrome azurol S) and fluorescence observation under violet light to screen siderophore producing bacteria were consistent. By the virtue of quantity and intensity of siderophore absorbance apex, it is concluded that different molecular structures of siderophore appeared under different pH values. In addition, pH 8.3, SM medium and C∶N ratio of 10∶1 represented the optimum to produce siderophore, respectively. Different exogenous amino acids had different effects on production of siderophore. Supernatant of siderophore had a significantly inhibitory effect on five different phytopathogenic moulds growth.