13～20 nm monolayer high quality GaAs thin films have been deposited by radio frequency (RF) magnetron sputtering technique in the atmosphere with hydrogen. The effect of hydrogen passivation on the micro-structure and optical properties of GaAs films was reported. The GaAs thin films were studied by X-ray diffraction,atomic force microscope pattern,absorption and photoluminescence (PL) spectrum.Experimental results show that the GaAs thin films have fcc zinc-blende structure,larger the granular size and more coarseness morphology,when the substrate temperature is at 500℃～520℃ with hydrogen or at 520℃ without hydrogen,a clear exciton hump and blue shift phenomenon were observed in the absorption spectra as well as a stronger peak were found in the PL spectra. These results indicate that hydrogen has passivation effect on GaAs thin films significantly.