The invention discloses a 300MW circulating fluidized bed boiler island device; the boiler of the invention adopts the circulating fluidized bed profile, limestone powders are added in the boiler and combusted at the temperature of 840 DEG C to 950 DEG C; the boiler comprises a separator, a material return system, a first-level raw coal crushing system, a second-level raw coal crushing system, a first-level coal feeder, a second-level coal feeder, an air-water combined fluidized type cold slag apparatus, a mechanical dry type slag removing system, a deoxidizing chamber and a coal bunker, wherein an outlet of the second-level coal feeder is provided with a helical type dispenser; the deoxidizing chamber and the coal bunker adopt the combination single frame arrangement, the deoxidizing chamber is provided with a built-in deaerator; the invention has the advantages of high efficiency, environmental protection, cleanliness, smooth slag removal, safety, reliability and high efficiency and energy save of the equipment; moreover, the coal feeding system is not blocked, all environmental protection emitting values of the boiler operation reach or exceed the National Environmental Protection Emission Standard, the main workshop arrangement of the invention is optimized, compact and reasonable, which meets the requirements of the production operation and the maintenance and the whole project is low in investment.