Ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM][PF₆]) was used as a plasticizer of acrolein-pentaerythritol resin (123 resin). The effect of [BMIM][PF₆] content under the condition of 0~10% on the plasticizing properties of 123 resin was studied. The comprehensive mechanical properties of cured 123 resin were studied by an universal testing machine and a dynamic mechanical analyzer (DMA) respectively.Results show that [BMIM][PF₆] can effectively improve the flowability of prepolymer of 123 resin, the effect is better than that of diethyl phthalate (DEP) and addition of 10% [BMIM][PF₆] can make the viscosity of 123 resin prepolymer at 50 ℃ reduce to 185 mPa·s. The more the [BMIM][PF₆] content, the greater the elongation at break and the lower the tensile strength of 123 resin cured products, and the elongation at break and tensile strength of 123 resin containing 10% [BMIM][PF₆] are 14.2% and 38.2 MPa, respectively. The glass transition temperature decreases and tenacity increases of 123 resin cured products with the increasing of [BMIM][PF₆] content in 123 resin.