Provided is a four-bottom three-cavity injector. A bearing seat and gas top cover integrated piece and a belt ring three-bottom and fuze integrated piece form a gas chamber; a chamber jointly definedby the belt ring three-bottom and fuze integrated piece and a belt ring two-bottom jointly is an oxidant chamber, an oxidant inlet section is an inlet of an oxidant and is communicated with an oxidantcollector, and the oxidant inlet section is provided with a flow deflector that divides an incoming flow oxidant into two strands that flow into the two sides of the oxidant collector respectively. Achamber defined by a belt ring two-bottom and a one-bottom is a fuel chamber, a fuel inlet section is a fuel inlet and is communicated with a fuel collector, and the fuel inlet section is provided with a flow deflector that divides incoming flow fuel into two strands that flow into the two sides of the fuel collector respectively; and nozzle assemblies are mounted on the belt ring three-bottom and fuze integrated piece, the belt ring two-bottom and the one-bottom. The gas chamber, the oxidant chamber and the fuel chamber are sequentially distributed from top to bottom.