This letter reports a theoretical and experimental investigation on high-power laser induced thermal blooming effect in a closed chamber with three different gases. In the theoretics, an incompressible gas turbulent model is adopted. The numerical simulation considers the gas refractive index as a function of both the temperature and pressure. The experiment is performed based on the pump-probe technology. A high power 1064 nm fiber laser with maximum output power of 12 kW is used to cause the gas thermal blooming, and a 50 mW high beam quality 637 nm laser diode (LD) is applied as a probe beam. The influence of the gas thermal blooming in the chamber on the probe beam wavefront and beam quality is analyzed for three different gases of air, nitrogen and helium, respectively. The results indicate that nitrogen is well suitable for restraining thermal blooming effect for high-power laser. The measured data are in close agreement with the simulated results.