Arsenic content in coal was determined by arsenic molybdenum blue spectrophotometry. The effects of reagent configuration, zinc particle size, color reaction time and coloration time on the determination process and results were studied. The results show that the detection reagent needs to be co - existing ,  zinc particle size is controlled 3 ~ 5 mm，the color reaction time in boiling water bath is 20 ~ 25 min, and the coloration time after cooling is below 3 h, thereby ensuring the accuracy of the results .