Methyl methacrylate(MMA) was polymerized in bulk solutions using low intensity ultrasonic radiation of 0.25 W/cm2.The factors affecting the polymerization(i.e.ultrasonic,PMMA granular,inhibitor and reaction ambience) were investigated,and the sample of polymer was characterized by gel permeation chromatography technique.The results mean that the reaction is initiated by free radicals and the radicals come from the friction between the macromolecule of PMMA and monomer of MMA.Several factors(i.e.the frequency of the ultrasonic,the time of irradiation) can strongly affect the polymerization rate.The product gained by the ultrasonic irradiation has a more regular molecular weight distribution and which contains scarcely any initiator,so the product has potential applications in some areas.