Abstract: The total amount of iron in iron replacement copper solution was measured at 419 nm by differential spectrophotometry with the chromogenic agent as sulfosalicylic acid and Fe³⁺ standard solution as reference solution. The effects of the different wavelength, chromogenic agent, the dosage of ammonia, the chromogenic time influence on the absorbance of the solution were investigated. The result shows that the best measurement conditions within 1h as follow: the absorption wavelength is 419 nm, the amount of 20 % sulfosalicylic acid is 15 mL, the amount of (1 + 1) ammonia is 15 mL. A linear regression equation of "C= 0.009 4Abs + 0.0159 5", is obtained, with correlation coefficient R²=0.999 4.The recovery of standard addition is 99.38 %~99.38 %, and the average recovery is 99.50 %.