The invention discloses a pressure sensitive adhesive and a preparation method thereof. The pressure sensitive adhesive is composed of the following raw material components including, by weight, 5-8 parts of butyl acrylate, 1-2 parts of styrene, 1-2 parts of methyl methacrylate, 0.1-1 part of alpha-methacrylic acid, 0.3-0.5 part of potassium peroxodisulfate, 4-15 parts of 2-butanone, 1-5 parts of chlorosulphonated polyethylene and 0.1-0.8 part of dioctyl phthalate. The preparation method of the pressure sensitive adhesive comprises the steps that firstly, the butyl acrylate, the styrene, the methyl methacrylate, the alpha-methacrylic acid and the 2-butanone are added in a stirring barrel; secondly, the potassium peroxodisulfate is added, the temperature is increased to the reaction temperature, and reaction is performed for 2 h; thirdly, when liquid in the barrel is colorless, transparent and sticky, the liquid is cooled to the room temperature, then the chlorosulphonated polyethylene and the dioctyl phthalate are added, and after mixing is performed for several time, filtering and discharging are performed. The pressure sensitive adhesive is high in transparency and viscosity, easy to process and convenient to coat, and has the heat resistance and weather resistance; the light transmittance of light rays is improved, and the reliability of the product performance is guaranteed.