CH4 concentration and CO2 separation from biogas (CH4/CO2) by an one-stage hydrate formation was supposed to be a prospective and economical practicable technology compared with traditional gas separation methods. We investigated the influence of 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM] PF6) on simulated biogas (64.0 mol %CH4/CO2) hydrate separation in this work. The thermodynamic promoter TBAB was combined with [BMIM] PF6 to investigate binary gas hydrate formation and separation efficiency. Different parameters which affected hydrate formation were investigated. The concentration of [BMIM] PF6 was 1000/2000/3000 ppm, and the optimized concentration of TBAB was 4 wt %. With respect to the hydrate gas separation results, the addition of TBAB can decrease CH4/CO2 hydrate formation pressure greatly and the hydrate formation induction time. CH4 in the remaining gas can be increased from 64.0 to 79.90 mol %, and CH4 recovery can arrive at 95.83%. Meanwhile, the addition of [BMIM] PF6 could increase the CO2 mole friction in hydrate from 36.0 to 58.63 mol %. So it was demonstrated that the combination of TBAB + [BMIM] PF6 would have a great application prospect on biogas purification technology.