Abstract: Basic principle and operation process of the determination of arsenic in feed-grade manganese sulfate by hydrogen arsenide generation followed by arsenic antimony molybdenum blue spectrophotometry were introduced.In operation process of the determination,first adopt hydrogen arsenide generation method to prepare arsine (AsH<SUB>3</SUB>);then use iodine solution to oxidize and absorb volatilized arsine;the quinquevalent arsenic solution was formed;add antimony molybdenum&nbsp; anti-chromogenic agent to form arsenic antimony molybdenum blue solution;finally the content of arsenic was determined by spectrophotometry.This method has met the accuracy and precision requirements of quality index testing method in Standard of Feed-grade Manganese Sulfate (mass fraction of As≤0.000 5%) HG 2936—1999,which can be popularized and applied in&nbsp; manganese sulfate manufacturing enterprises.