The invention provides a gas injection type rotary detonation ramjet combustion chamber. The combustion chamber is a cavity defined by a shell and a center body arranged in the shell, wherein the shell is in a hollow cylinder shape, the two ends of the shell are open, the cavity comprises an air inlet channel, an isolation section channel, a mixing channel, an expansion channel, a combustion chamber cavity body, a combustion chamber throat and an exhaust nozzle which sequentially communicate, fuel nozzles are arranged at the expansion channel and / or the combustion chamber cavity body, and an annular rocket is arranged at the isolation section channel. According to the gas injection type rotary detonation ramjet combustion chamber, air is mixed and pressurized through the annular rocket, mixed airflow is converted into subsonic velocity from supersonic velocity in the expansion section, and a throttling section is formed, so that pulsating pressure generated in the combustion process ofthe combustion chamber is prevented from being transmitted to the upstream; and meanwhile, the annular rocket is adopted for ejection and pressurization, so that the combustion efficiency of the combustion chamber is improved, the flight envelope range of a rotary detonation ramjet is widened, an aircraft can normally work when the flight Mach number is low, and stable thrust is provided for theaircraft.