Space-based laser radar (lidar) technology is widely acknowledged as an indispensable detection method in critical fields such as geospatial mapping and national defense. The 532 nm/1064 nm dual-band reflectance coating constitutes a vital component within lidar systems, performing essential functions in optical path transmission and the regulation of spectral efficiency. Electron beam evaporation (EB) is the predominant technique employed for the fabrication of HfO₂/SiO₂ dual-band reflective coatings, which are characterized by high damage thresholds. However, due to the inherent limitations of the fabrication process, HfO₂/SiO₂ thin films typically exhibit a porous and loosely compacted microstructure, rendering them highly susceptible to the adsorption of water vapor under atmospheric conditions. The subsequent desorption of this water vapor under vacuum operating environments leads to spectral shifts within the thin films, which significantly compromises the operational stability and performance reliability of the laser radar system. Therefore, it is necessary to improve the current preparation method to meet the needs of different usage environments. For this purpose, a waterproof vapor laser film is designed in this paper.The HfO₂/SiO₂ multilayer film is designed and fabricated using electron beam evaporation, followed by the deposition of a 20 nm Al₂O₃ layer on the top and side walls of the multilayer as a water vapor barrier, using atomic layer deposition (ALD) (Fig.3). The performance of the water vapor barrier is evaluated by testing the spectral characteristics in both vacuum and atmospheric conditions (Fig.4). The laser damage threshold at 1064 nm and 532 nm is assessed using a Nd:YAG laser to evaluate the laser performance (Fig.5).Upon testing the thin films under both vacuum and atmospheric conditions, it is observed that the films fabricated via the electron beam (EB) process exhibit an average overall drift of approximately 2.5% at the central wavelengths of 1064 nm and 532 nm (Fig.4(a)). In contrast, when the top and side walls are coated with a 20 nm layer of ALD-Al₂O₃, only a negligible drift of 0.3% is observed (Fig.4(b)). This demonstrates excellent vapor barrier performance. Moreover, the bandwidth of the samples remains stable in both atmospheric and vacuum conditions, with no discernible reduction in reflection efficiency following the deposition of the ALD-Al₂O₃ layer in the vacuum environment. Furthermore, the damage threshold of the multilayer film with the ALD-Al₂O₃ coating (13.1 J/cm²) is found to be slightly lower than that of the multilayer film without the ALD-Al₂O₃ coating under 532 nm laser irradiation (15.7 J/cm²) (Fig.5(a)-5(b)). Under 1 064 nm laser irradiation, the damage threshold of the multilayer film after ALD-Al₂O₃ coverage (41.5 J/cm²) is observed to be marginally lower than that of the uncoated film (44.5 J/cm²) (Fig.5(c)-5(d)). The current results are sufficient to fulfill the practical operational requirements.A waterproof vapor laser film has been prepared. Due to the dense microstructure of the Al₂O₃ film prepared by atomic layer deposition, it was covered on the top and sidewalls of the HfO₂/SiO₂ multilayer film prepared by electron beam evaporation. Testing the spectrum under atmospheric-vacuum conditions showed that the drift caused by water vapor decreased from 2.5% to 0.3%, demonstrating good water vapor barrier performance. Additionally, the laser damage threshold test of the film showed that after covering with the ALD film, the threshold decreased from 15.7 J/cm² at 532 nm to 13.1 J/cm², and from 44.5 J/cm² at 1064 nm to 41.5 J/cm². This may be due to defect attachment during the transport process. Nevertheless, this waterproof vapor laser film still meets operational requirements and enhances atmospheric-vacuum stability.