Abstract: Mid-wave(MW) antireflective films were coated on double-side polished Ge substrate, and the films were experimented in hygrothermal environment for sustaining 24 h,224 h,324 h,424 h,524 h,724 h,,1224 h,respectively. The effects of hygrothermal environment on the reliability including transmittance and adhesion of Gebased MW antireflective films were studied .The results indicate that , the transmittance of MW antireflective films becomes lower gradually after sustained in the hygrothermal environment, and the absorption peak of CO2 and H2O turnes up , resulted from the increase of the content of CO2 and H2O in the films sustained under hygrothermal environment for enough time; The fringe of film becomes desquamated after 1024 h in hygrothermal environment ,and from that time,the average transmittance is lower than 85%.