The inclusion complex of methyl methacrylate（MMA） with randomly methylated β-cyclodextrin (RAMEB) was synthesized by solvent method and characterized by TG-DSC, UV．Molar ratio method shows that the 1∶1 inclusion compound has formed between RAMEB and MMA. TG –DSC analysis shows that RAMEB and MMA have formed steady inclusion and the stability of MMA has increased remarkably. Using MMA as monomer, K2S2O8 as initiator, we investigated the influence of RAMEB on the sope-free emulsion polymerization of MMA. It is found that when the addition of RAMEB is 0.5g, the conversion of MMA reached 89.21% in 30min at 75℃. Compared to no addition of RAMEB, the conversion increased 30.6%. When the addition of RAMEB is 1g, the polymerization speed decelerated and monomer conversion was almost the same compared to no addition of RAMEB. The addition of RAMEB increased particle size of PMMA. With the increase of RAMEB, PMMA particles are getting more and more uniform.