In order to study the effect of fatty acid unsaturation on flotation of low-rank coal, oleic acid, linoleic acid and linolenic acid with the same number of carbon atoms but increasing number of double bonds were selected as flotation collectors, and compared with conventional nonpolar collector diesel oil. The measurement of adhesion force between particles and bubbles and molecular dynamics simulation of reagent adsorption were used to reveal the mechanism of unsaturated fatty acids enhancing flotation of low-rank coal. The flotation results show that the flotation performance of unsaturated fatty acid collectors is better than that of nonpolar diesel oil, and the flotation yield of low-rank coal increases with the increase of fatty acid unsaturation. Scanning electron microscopy (SEM), infrared spectroscopy (FTIR) and x-ray photoelectron spectroscopy (XPS) were used to analyze the surface morphology and surface functional groups of the low-rank coal. SEM results show that the surface of low-rank coal is loose and contains a large number of pores and cracks, which is not conducive to the spreading of chemicals on coal surface and the mineralization of bubbles and particles. The results of FTIR and XPS show that the surface of low-rank coal contains a large number of oxygen-containing functional groups (-OH and C-O), and surface hydrophobicity of coal samples is poor, resulting in low flotation recovery. The adhesion force between bubble and coal surface in different collector solutions was measured. The maximum adhesion between bubble and coal surface increased with the increase of collector unsaturation in diesel oil, oleic acid, linoleic acid and linolenic acid systems, which indicated that the floatability of coal particles increased with the increase of collector unsaturation. Furthermore, the molecular dynamics simulation of unsaturated fatty acids adsorption was analyzed, and the results showed that unsaturated fatty acids spread on coal surface through hydrogen bonding between their polar groups and the polar groups on coal surface. With the increase number of double bonds, the polarity of unsaturated fatty acids increases, and the adsorption degree of unsaturated fatty acids on coal surface increases gradually, which leads to the increase of particle floatability. It is the main reason for the increase of flotation recovery of low-rank coal with the increase of unsaturated fatty acids.