The invention belongs to the field of PVC (Polyvinyl Chloride), particularly discloses a production method of the modified PVC, and also discloses a production device of the modified PVC. The production method of the modified PVC comprises the following steps: simultaneously adding a vinyl chloride monomer (VCM), cold water and hot water into a reactor during material feeding, and enabling the temperature in the reactor to be kept at 55 to 60DEG C; introducing cooling water into a reactor jacket in the reaction process, introducing the cooling water into a condenser at the top of the reactor, and enabling the temperature of the reactor to be kept at 55 to 60DEG C. According to the production method of the modified PVC, disclosed by the invention, the cold water and the hot water are simultaneously added during the material feeding, the temperature of materials in the reactor is kept below polymerization reaction temperature, the step of raising the temperature of hot water is omitted, the material feeding time is shortened, and the capacity of the reactor is improved; the reaction temperature of the reactor is kept constant, a polymerization reaction is enabled to be performed at constant temperature, and the reaction is more stable; prepared PVC particles are loose in shape, and the VCM left in the particles is favorably stripped by steam; the residual quantity of VCM in the PVC particles is stabilized within 5PPm, and the requirement of food grade is met.