Infrared solar spectra on clear days were measured automatically by an infrared solar spectrometer (ISS) capable of 0.4 cm-(-1) resolution developed by us. Precipitable water was retrieved from the recorded infrared solar spectra near 3.434 μm wavelength band,which is absorbed by atmospheric water vapor. Comparison shows that the retrieval result coincides quite well with radiosonde. The characteristics of diurnal and seasonal variation of precipitable water were obtained over Hefei from the measuremental data of nearly 18 months since April of 1997. It is found that the precipitable water is related to surface dew point temperature. The results are also discussed in the paper.