Based on reaction of o-phthalaldehyde（OPA）-NH3-sulfite system,a solid-phase fluorescence spectrometric method was established for the determination of ammonia nitrogen in natural water sample using filter paper as solid support.Experimental parameters such as soaked time of the filter paper,pH value and reaction time were optimized.The optimal conditions were as follows:soaked time of filter paper:＞4 h;pH value:11.5-13.0;reaction equilibrium time:165 min.Under the optimized experimental conditions,the calibration curve was linear in the range of 2.00-12.0 μmol/L,with a detection limit of 0.746 μmol/L.The spiked recoveries were in the range of 89.6%-101.6% for spring water and river water.The proposed method was applied in the detection of ammonia nitrogen in fourteen river water samples,and the results were consistent with those obtained from the indophenol blue method.