Low-rank coal has poor surface hydrophobicity, resulting in low flotation efficiency. As a pretreatment process before flotation, conditioning could improve the dispersion of non-polar oil and the hydrophobicity of particle surface, thus effectively improving the flotation effect. The influence of conditioning speed and time on the flotation of low-rank coal was studied by using low-rank coal from a coal preparation plant in Inner Mongolia. The effect of conditioning on the surface properties of coal particles was analyzed by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and contact angle analyzer. The results showed that the yield and ash content of clean coal increased with the increase of condition speed and time. When the amount of diesel oil was 7 kg/t, the condition speed was 2400 r/min, and the conditioning time is 1 min, the combustible recovery and flotation perfection index reached the maximum. The contact angle of the coal particle surface gradually increased with increasing conditioning speed, but when the speed was too high, the contact angle decreases slightly. Compared with the coal sample before conditioning, the carbon content on the surface of the coal sample increased after conditioning, the C-C/C-H functional group content increased, the C-O functional group content decreased, and the surface hydrophobicity of the coal sample increased. The increase of conditioning speed increased the dispersion of non-polar oil and the probability of collision between the collector and coal particles. However, the shear force may cause the desorption of the agent adsorbed on the surface of the coal particles, thereby reducing the flotation effect at overhigh conditioning speed.