The invention relates to pH (potential of Hydrogen) independent polymethacrylate. The pH independent polymethacrylate is a terpolymer of ethyl acrylate, methyl methacrylate and methacrylic acid chlorinated trimethylamine ethyl ester, and is prepared through copolymerization by taking dimethyl 2,2'-azobis (2-methylpropionate) (AIBME) as an initiator and ethanol as a solvent, wherein the weight ratio of ethyl acrylate to methyl methacrylate to methacrylic acid chlorinated trimethylamine ethyl ester to AIBME to ethanol is 1:(1.688-2.012):(0.202-0.598):(0.0256-0.0365):(1.369-2.568). The invention also provides a preparation method of the pH independent polymethacrylate. The polymethacrylate copolymer disclosed by the invention is insoluble in acid solution or alkaline solution and not related to the pH of dissolving environment. The pH independent polymethacrylate can be used after being mixed with some water soluble substances and the dissolving of the mixture can be realized through controlling the dissolving of the water soluble substances, so that the controlled release of wrapped drugs is realized. The preparation method provided by the invention is reasonable in design, simple and convenient in operation and capable of effectively guaranteeing the product quality.