The absorption spectra, fluorescent spectra and fluorescent lifetime of Yb3+-doped phosphate glasses were measured. Three measure methods for the fluorescent lifetime were also presented. The effects of OH groups, alkali oxides, Yb3+ ions and glass contents et al on the fluorescent lifetime were studied. The results indicated that the fluorescent lifetime of Yb3+-doped phosphate glasses is desreased via the mechanisms of shorting meta-stable state lifetime, increasing the NBO number, lifetime quenching and non-radiation transition respectively.