Abstract: Numerical simulation of chemical oxygen iodine laser (COIL) gases flows based on RADICL setup with vapor condensation was carried out, in which the materials and energy sources caused by vapor condensation were incorporated into our 3-D code, and the number density of drops were given. The pressure, temperature, and gain obtained with condensation were compared with those without condensation. It was found that under vapor condensation,the gases temprature and the peak of gain rise near the downstream nozzle throat.