The experimental study of the dielectric coating for deformable mirrors in COIL laser system is reported. The coating Sub/Ag(SiO2/HfO2)4/Air and Sub/Ag(YbF3/ZnS)3/air have been manufactured in high vacuum deposition chamber. The optical and physical properties of high reflectance dielectric coatings subjected to a large number of deformation cycles are determined. The reflectance of these mirrors is 99.90% and 99.87% respectively. The physical properties of the deformable mirrors have not been changed under deformable cycle 109 times. The thermal distortion and laser induced damage of deformable mirror irradiated with COIL laser are investigated. It is concluded that 1kw/cm2 laser power density is safe and reliable for these deformable mirrors in COIL laser system.