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In order to realize the rapid and accurate determination of the ammonia nitrogen content in the aquaculture water, the ammonia nitrogen in the water was taken as the research object, and the colorimetric sensing experiment was carried out on the basis of the salicylic acid spectrophotometry combined with the microfluidic technology to realize the quantification of the ammonia nitrogen content in the solution detection. By comparing the influence of four characteristic wavelength screening methods on modeling, it was found that the continuous projection algorithm selected the least wavelength variables, and the established prediction model had the best effect. The modeling set calibration standard deviation (RMSEC) and the prediction set calibration standard deviation (RMSEP) were 0.00931mg/L and 0.02857mg/L, respectively, and the relative analytical error (RPD) was 11.2141. The effects of pH value, salinity, temperature and reagent stability were explored, and it was found that the absorbance was increased first and then decreased with the increase of pH value. The salinity had a significant effect, and temperature can speed up the reaction, and the reagents can be stored for 14 days at 6℃ in dark. Under optimized conditions, the linear range and detection limit of the method were 0.04~0.92mg/L and 0.016mg/L, respectively. The standard recovery experiment was carried out on aquaculture water and seawater. The average recovery rate was between 95.8% and 116%, and the relative standard deviation was between 2.1% and 6.3%. The results proved the feasibility of the method of using salicylic acid spectrophotometry combined with microfluidic technology to detect ammonia nitrogen.