Abstract: This paper deals with ion flotation spectrophotomtric detrmination of trace amount sulfide ion in water with modified simplex method (MSM) of multifactor optimiztion control by means of IBM-PC computer. The optimization condition of enrichment and determination can be obtained. The determining range of linearity of sulfide ion concentration was 0.002-0.04mg/L. The recovery ratio of this method was 92%-99%, the relative standard deviation was less than 1.3%, and the limit of detection was 0.0005 mg/L. This method has a good feasibility. reproducibility, precision and satisfactory recovery ratio.