This paper introduces a process technology of making antimony trisuifide ultrafine using bidirectional revolving ball mill.By experiment,the influences of the amount of material feed,the addition of alcohol,the ratio of ball to powder,milling time and the rotational speed rate of outer cylinder etc on the particle size of antimony trisulfide powder were analyzed,the optimum process conditions were searched out.The particle size the antimony trisulfide powder that was prepared under the optimum process conditions achieves D90 < 10μm,can meet the technical requirements of delay composition production.