The invention provides an apparatus and process for producing a chlorinated high polymer. According to the invention, plasma or ultraviolet lamps are used to excite chlorine gas so as to prepare the chlorinated high polymer. Under the action of fluidization gas and fluidization-aiding gas, the chlorinated high polymer is produced by a pretreated high polymer under the excitation of plasma or ultraviolet light through stirring and heating, wherein the fluidization gas is composed of pretreated chlorine gas and hydrogen chloride gas or inert gas in proportion. Due to the gradient control of the chlorination reaction heat, two or more fluidized bed reactors are installed in the apparatus and connected by risers which are easy to adjust length and each of which is internally provided with an ultraviolet light tube or a plasma discharging device, wherein the risers are mainly used for exciting reaction gas, prolonging gas activation time, dissipating heat and promoting uniform reaction. The high polymer and the reaction gas circulate between the two fluidized bed reactors through the risers, so the phenomenon of uneven chlorination caused by backmixing occurred in single-bed fluidization can be avoided and the phenomenon of non-smooth movement of materials caused by the height restriction of a high polymer layer can be overcome; and thus, reaction heat is better controlled, and the high polymer meets the requirement of uniform chlorine content.