Aiming at the thermal management problem of the gain generator in the chemical laser, a phase-change cooling system for the gain generator has been designed on the premise of keeping the original water-cooling channel unchanged. The phase-change microcapsule suspension with a phase-change temperature 43 ℃ is selected as the cooling medium. The system eliminates the bulky water tank and water pump in the water-cooling system, achieving miniaturization and lightweight of the cooling system for the gain generator of the chemical laser. By comparing the cooling effect of the phase-change microcapsule suspension with that of water-cooling through experimental research, using the stable combustion chamber pressure as the standard for judging the cooling effectiveness, the effect of micro-encapsulated phasechange materials suspension on the cooling of the gain generator in the chemical laser has been investigated. The experimental results have shown that the gain generator cooling system using the phase-change microcapsule suspension with a phase-change temperature of 43 ℃ can effectively cool the kilowatt-level chemical laser.