The invention relates to a preparation method for a waterproof laser film. According to the requirement in practical application of normal incidence 800nm pumping transmission and back incidence 1064nm fundamental frequency light reflection, an HfO2 and SiO2 film is prepared by a vacuum electron beam evaporation sedimentation technology and is taken as the film which has a large electric filed and is easy to damage due to being close to a base plate when being used as the back incidence, so as to obtain higher laser damage resistance threshold; aiming at the working condition of a water cooling system, for the films close to the water side and easy to be permeated and corroded, Ta2O5 and SiO2 films are prepared by an ion beam auxiliary sedimentation technology, so that the microstructure of the film is improved, higher stacking density is obtained, and good waterproof performance is realized; HfO2, Ta2O5 and SiO2 of high or low refractive index are deposited alternately so as to form a multi-layer film, and the optical thickness of each layer is controlled so as to obtain the needed spectral characteristic. The preparation method can well take advantages of the three characteristics and can apply the characteristics to a neodymium glass substrate of a diode pumping solid laser system, so that the diode pumping solid laser system can work in a water cooing system normally, and has good laser damage resistance performance and the spectral characteristic needed by the system.