The invention discloses a cyclone separation water treatment apparatus and a water treatment method. A reaction tank is connected with the input end of a heating furnace through a sewage tube, the output end of the heating furnace is connected with the water inlet tube of a cyclone separator, the bottom sewage outlet of the cyclone separator is connected with the reaction tank through a sewage circulating tube, and a steam outlet at the top of the cyclone separator is connected with a water storage tank through a steam pipeline; and the tank body of the cyclone separator is sequentially provided with the steam outlet, a flow guiding cylinder, the water inlet tube, a helical groove, a dewhirl device and the sewage outlet from top to bottom. The cyclone separation water treatment apparatus and the water treatment method allow heated sewage in a gas and liquid coexistence state to be transmitted to the cyclone separator and to be separated, and separated steam liquid drops are output through the steam outlet in order to complete purifying treatment.