Abstract: In view of the difficulty in flotation of low-rank coal, experimental study is conducted on the promoting effect on flotation of such coal produced by different collectors. Response Surface Methodology(RSE) is used to optimize the experimental design. The experimental design and data analysis are made by using the Design Expert 8.0 software with dosage of collector and frother, and proportioning of agents as influence factors. As indicated by study results, the dosages of collector and forther exert a significant impact on flotation performance; and with a mass percent of compound agent of Span80 at 20%, a dosage of collector at 3 600 g/t and a dosage of frother at 770 g/t, the yield and ash of flotation concentrate, ash of tailing and recovery of combustible matters are 83.06%, 11.62%, 67.99% and 93.12%, respectively, with a noticeably improved flotation effects as compared with the case without the use of compound agent. It is noted through XPS analysis and analysis of variation of contact angles of the coal sample before and after the compound agent goes into action, the addition of compound agent can lead to reduction of oxygen-containing functional groups on coal surface, increase of both contact angle and hydrophobicity and promotion of interaction with kerosene, thus beneficial to improvement of flotation efficiency.