The separation of ultrafine coal is inefficient due to the low settling velocity in centrifugal field. The feasibility of increasing particle size by flocculation to increase the separation efficiency is verified. The effect of flocculant on the size distribution of ultrafine coal was tested. The effect of flocculant dose on deash and desulfurization efficiency was studied to determine the appropriate dosage. Further, influence of the main operating parameters of the concentrator, including centrifugal force and water counter pressure on the separation performance, was studied. In addition, a comparative test was designed to verify the stability of the flocs. Results showed that the size of ultrafine coal particles could be effectively increased by the addition of flocculant, and the yield of -0.045 mu m fraction was decreased from 50% to 17% when the flocculant dosage was 10g/t. The combustible material recovery of clean coal increased from 58% to 66%; meanwhile, the ash content reduced from 16.7% to 14.6%. In addition, combustible matter recovery and desulphurization efficiency decreased with the increase of centrifugal force, while they increased with the water counter pressure. Results of comparison tests of ultrafine coal with flocculant pretreatment and artificial coal with the same size composition showed that the latter had greater combustible recovery and desulfurization efficiency.