The invention provides a device and method for preparing tetrafluoroethylene and hexafluoropropylene through cracking monochlorodifluoromethane. The device comprises an air inlet cavity which is arranged at the upper end of the device, a reaction cavity communicated with the lower part of the air inlet cavity, a cooling cavity communicated with the lower part of the reaction cavity, and an air outlet cavity communicated with the lower part of the cooling cavity, wherein the air inlet cavity is wider than the reaction cavity; the air outlet cavity is wider than the reaction cavity; the reaction cavity is F in width, Al in height and W1 in length; a heating body is arranged outside the reaction cavity. The method comprises the steps: cracking monochlorodifluoromethane gas to obtain tetrafluoroethylene gas, and further cracking the tetrafluoroethylene gas to obtain hexafluoropropylene; and cooling and outputting the hexafluoropropylene. According to the device and the method provided by the invention, the investment cost is greatly reduced, the safety is improved and energy is saved; gas generated from side reaction can be repeatedly used, the cost is saved and the environment is protected.