Abstract: Polymerization of methyl methacrylate in magnetic fields influences the syndiotacticity in the molecular chain of polymethylmethacrylate. By increase of magnetic field intensity, the percent content of the syndiotactic of polymethylmethacrylate increases, and so does glass temperature.The composition probability of N chain segments of the syndiotactic of polymethylmethacrylate in the molecular chain of polymethylmethacrylate can also be calculated.