Laser ignition characteristics of composite modified double-base (CMDB) propellant containing hexanitrohexaazaisowurtzitane (CL-20) are researched by CO2 laser beam at different laser power densities. The effects of Al powder content and burning-rate catalysts on ignition characteristics of CL-20-CMDB propellants are discussed. The results show that the laser ignition delay time of CL-20-CMDB propellants without catalyst decreases with the increase of power density, the change of delay time becomes small at high power density and the ignition process of the propellants has hardly any variety when the heat flux is in the range of 25.5~127.0 W/cm2. The delay time and the ignition process of the propellants containing catalysts have a close dependence on the laser flux. The ignition appears in the gas phase near the propellant surface and the ignition delay time becomes longer at high power density. The content of Al powder has strong effect on the ignition delay time at the lower power density, but the action becomes weak with the laser flux increasing.