Azo dyes have strong hydrophilic and good adhesion to solid surface. In this study, 23 kinds of typical azo compounds were tested as depressant of sulfide minerals. Absorption of azo compound on mineral surfaces was detected by UV. The result shows that some of them can be good depressants of single sulfide minerals. With the number of azo group increasing from 1 to 3, depression performances are improved. On the other hand, depression performances of azo dye are related to the type of group and the location of phenyls，the results of adsorption and the frontier molecular orbital energy calculation may be used to explain depression performances of azo dyes.