In order to study the effect of subatmospheric pressures on the ignition and combustion characteristics of Al/Mg fuel-rich propellant, the propellant was ignited by CO₂ laser with different heat fluxes (1.26, 1.86, 2.23, 2.79 W·mm^-2) at subatmospheric pressures (0.01, 0.02, 0.04, 0.06, 0.08, 0.1 MPa). The ignition and combustion process of propellant was recorded by a high speed camera. The ignition delay time was obtained by two photodiodes which monitor the laser signal and flame signal. The effect of subatmospheric pressures on the ignition delay time, combustion process and linear burning rate of the propellant was discussed. Results show that the pressure influences the diffusion of the pyrolytic gases. The initial flame forms the shape of a cylinder when pressure is 0.08 MPa, as pressure decreases to 0.02 MPa, the shape of initial flame changes to be spherical. The reduction in pressure causes a longer ignition delay time, however, as the heat flux increases, the effect of pressure on the ignition delay time is significantly reduced. The burning rate decreases with the reduction of pressure and it decreases by 47% when the pressure drops from 0.1 MPa to 0.01 MPa. The Vielle burning rate formula shows a good agreement with burning rate data. Therefore, the Vielle burning rate formula is more suitable for characterization of Al/Mg fuel-rich propellant burning rate characteristics at subatmospheric pressures environment.