Abstract: A method of flow injection analysis was used for simultaneous determination of ammonia nitrogen and phosphate in seawater. Under optimized conditions,the linear ranges of ammonia nitrogen and phosphate were found in the range within 0.25 mg·L-1 and 0.30 mg·L-1,with detection limits (3S/N) of 0.42 μg·L-1 and 0.56 μg·L-1,respectively. The recovery rates measured by standard addition method were in the ranges of 85.0%-103% and 86.7%-103% for ammonia nitrogen and phosphate,respectively,with RSD were in the ranges of 0.43%-5.3% and 0-4.1%,respectively. The method was used to analyze standard substance,giving results in agreement with those obtained by spectrophotometry.