Abstract: In order to treat arsenic in waste acid, barium sulfide was used as arsenic removal agent. Indirection vulcanization and direct vulcanization were adopted to treat arsenic in waste acid successively. In the first stage of the process, waste acid reacted for 80 minutes at 50 ℃ when dosage of barium sulfide was 2.4 times of the theoretical calculations. In the second stage of the process, waste acid reacted for 60 minutes at 25 ℃ when barium sulfide was 1.6 times of the theoretical calculations. The result showed that the concentration of arsenic in waste acid decreased from 8 810 mg/L to less than 0.5 mg/L, achieving a comprehensive arsenic removal rate of 99.99%. Orthogonal experiment indicated that the dosage of barium sulfide was the most important factor affecting the removal of arsenic from waste acid, followed by reaction temperature and reaction time. The amount of sulfur slag produced in this process was small, which could greatly reduce the stacking pressure of the enterprises. And the barium sulfide generated in the process could be reused to reduce the production cost of the enterprises. At the same time, no new impure ions were introduced into the liquid after the second stage of arsenic removal, which reduced the subsequent treatment process.