Abstract: The influences of montmorillonite on coal flotation and the effects of sodium hexametaphosphate on the dispersion of fine clay mineral in coal flotation were investigated by wet contact angle and zeta potential measurement. Based on the theoretical calculation of EDLVO,the mechanism of montmorillonite and coal flotation in the presence of dispersant was analyzed. The results show that montmorillonite significantly inhibites coal flotation,and lower the combustible recovery of clean coal from 44. 11% to 11. 68% . Sodium hexametaphosphate can improve the performance of flotation by increasing 2 percentage of the combustible recovery. By adhering to the surface of coal particles and montmorillonite mineral particles,sodium hexametaphosphate increases the absolute value of zeta potential of the mineral to enhance the electrostatic repulsion,and it improves the hydrophilic polarization effect,strengthening the hydrophilic repulsion. Moreover,long-chain molecules formed from sodium hexametaphosphate hydrolysis adsorb on the particle surface,generating dimensional stabilization effect and increasing the steric hindrance when the particles approach to each other.