Fluorite and calcite have similar surface properties and natural floatability, so their flotation separation has always been a problem faced by the beneficiation industry. The key to flotation separation is the choice of depressants. Sodium hexametaphosphate (SHMP) has a good effect on fluorite calcite selective inhibition. In this paper, the effects of Zn²⁺ on the selective inhibition of SHMP in the flotation process of fluorite and calcite were studied through single mineral and artificial mixed mineral flotation experiments. Solution chemical calculation, X-ray photoelectron spectroscopy (XPS), Fourier Transform Infrared spectroscopy (FT-IR) and Time of Flight Secondary Ion Mass Spectrometry (ToF-SIMS) analyses investigated the mechanism of action of Zn²⁺, which had the most significant negative effect on the selective inhibition of SHMP. The results show that the main components of SHMP inhibiting minerals are HPO₄^2- and H₂PO^4-, which can react with Ca active sites on the mineral surface to form hydrophilic Ca(H₂PO₄)₂ and CaHPO₄, while Zn²⁺ The presence of HPO₄^2- in solution resulted in the formation of stable ZnHPO₄ complexes, thereby weakening the inhibitory effect of SHMP on minerals.