Abstract: The conditions and factors influencing of 18F－are investigated. It is producted by 18O (p,n) 18F with TR19 cyclotron(made in EBCO Company, Canada). The results show that the more abundance of target water, the more yield of 18F－,when the proton beam current is 10～35 µA and the irradiation time is in 20～60 min, the yield of 18F－ is increased with the added of the proton beam current and irradiation time. Thus, the abundance of target water, proton beam current, irradiation time are the main factors affected the yield of 18F－, at the irradiation same time. The parameters of ion source and main magnet is setted properly, in order to increase the yield of 18F－ and enhence the work efficency.