A numerical analysis has been developed to study the laser-induced ignition of nitramine propellants with both condensed-phase and gas-phase absorption. The analysis is based on the time-dependent conservation equations of mass, energy, and species concentration in both the gas and condensed phases. A comprehensive chemical kinetics scheme involving 45 species and 232 steps is used to study the detailed heat-release mechanism in the gas phase. The analysis has been applied to investigate the ignition delay and key chemical processes involved in the laser-induced ignition of HMX monopropellant. Results show gas-phase absorption of laser energy enhances the ignition process, but reduces the dependency of ignition delay on the laser intensity. The process consists of inert heating, thermal decomposition, primary-flame occurrence, secondary-flame preparation and formation, and, finally, establishment of steady-state combustion.