Abstract: This paper studies the causes for the low determination results of sulfide in water by methylene blue spectrophotometry. The experimental water,the experimental reagent,the experimental speed and the color developing time are analyzed and compared respectively. The results show that under the optimal experimental conditions determined by the experimental analysis,the calibration curve is linear,the correlation coefficient is 0.999,and the quality control samples are all within the guaranteed range. The relative standard deviation （RSD） is 1.0% （n = 6）.

Key words: sulfide in water, methylene blue spectrophotometry, experimental water, experimental reagent, color reaction time