In this paper, the effect of C3H6N6modified by imidazolium based Ionic Liquid 1-butyl-methylimidazolium hexafluorophosphate ([BMIM]PF6) on polyurethane rigid foam flame retardant properties was conducted.The results show that the flame retardant properties of C3H6N6 modified with Ionic Liquid significantly increased and the LOI increased form 22.3 to 24.5. In the modification process, the ionic liquid mass have a very noticeable effect to the flame retardant property and when [BMIM]PF6 and C3H6N6 in quality was 4:6, Fire-retardant effect was best.Compared with the prior to the modification, C3H6N6 modified can increase effective Flame resistance of materials, horizontal burning speed from 67.6mm/min down to 33.4mm/min.Thermal degradation data show that C3H6N6 modified could improve initial decomposition temperature and reminder yield of rigid polyurethane foam,and then heat release reduced, the decomposition controlled,thermal stability increased.