Abstract: The results of infrared spectrum indicate that the structure of the synthesis of xanthate organic depressant consist of -CSS-and has several hydrophilic groups. This paper studies the effect of the Cu²⁺ ion, the number of hydrophilic groups as well as the HLB of the synthesis of xanthate on depressing ability to pyrrhotite with flotation test. The inhibition mechanism of organic depressant is analyzed. The results of the experiment show that the depressing ability is still good in case of the presence of Cu²⁺ ion, in the pH range of 6-10, the depressing effect become stable. With the increase of the HLB and the number of hydrophilic group of xanthate, the depressing effect will be enhanced.