High reflective (HR) films with low stress and high damage threshold are deposited on a high-density deformable mirror (HDM) for a high-power laser system. The parameters of the laser system are about 5 J, 6 ns, and 200 Hz @ 1064 nm. The surface figure of the HDM is measured before and after coating, respectively. After coating, the surface error of HDM is only 39-nm rms, and the results show that the residual stress of HR films is very small. Then, a Φ50-mm sample and the HDM are tested successively in the high-power laser system. The temperature rise of the sample and HDM are measured in real-time. Finally, the temperature of HDM has risen by 10°C, while the sample is changed by only 1°C.