Abstract: In order to evaluate the uncertainty of measurement of acid soluble ferrous content in iron ores by potassium dichromate redox titration，a mathematical evaluation model was established through sample pretreatment，chemical reaction process and titration of potassium dichromate and acid soluble ferrous. Through Cochrane test，it was concluded that there was no significant difference in the daily detection accuracy of acid-soluble ferrous iron，and regression analysis showed that there was no significant correla⁃ tion between the standard deviation and acid-soluble ferrous iron content. The combined sample standard deviation was taken as the Type A uncertainty. The source of Type B uncertainty mainly involves the errors of balance，burette and volumetric bottle，etc. They are quantified one by one and synthesized by mathe⁃ matical model，so as to calculate the synthetic uncertainty and extended uncertainty.Finally，the measured value of ferrous oxide is between 0.2% and 20%，and the Type A uncertainty of a single test is 0.06%. During the evaluation process，it was found that the titration volume was the largest source of uncertainty. The experimental improvement measures were to appropriately expand the titration volume and use a buret with higher accuracy.

Key words: iron ore, acid soluble ferrous, uncertainty, inclusion probability