Abstract: Objective To explore the enhancing effect of sodium hexametaphosphate as an inhibitor on the flotation performance of low-rank coal slime and its mechanism of strengthening flotation, Method The flotation experiment was conducted with low-rank coal slime as the research object and sodium hexametaphosphate as the inhibitor, and the influence of sodium hexametaphosphate dosage on the flotation indexes was investigated. The enhanced flotation mechanism was analyzed based on the contact angle test, Zeta potential test and EDLVO theory. Result When the dosage of sodium hexametaphosphate was 800 g/t, the flotation indexes of low-rank slime were relatively good, the cleaned coal yield, ash content, combustible recovery and flotation perfection index were 53.95%, 30.25%, 87.33% and 46.92%, respectively, the cleaned coal yield increased by 6.24 percentage points, the ash content increased by 6.24 percentage points, the combustible recovery increased by 17.01 percentage points, and the flotation perfection index increased by 15.14 percentage points. The contact angle of low-rank coal slime increased by 18.1°, and the Zeta potential values were significantly increased. Conclusion Sodium hexametaphosphate mainly acted on the mineral surface through electrostatic force to enhance the electrostatic repulsion between particles, reducing the cover of kaolinite and quartz on low-rank coal slime and making the flotation system more dispersed, and so as to obtain better flotation effect.