The invention discloses an e-beam bombardment resistant secondary electron emission composite film and a preparation method thereof, and belongs to the technical field of preparation of functional film materials. By using high-pure metal silver as a substrate material, a magnesium aluminum alloy in a certain atomic ratio as a sputtering source material and high-pure argon-oxygen mixed gas as working and reaction gas, a direct-current reaction magnetron sputtering coating technology is adopted under a certain temperature condition, by adjusting parameters such as sputtering power, sedimentationtime, gas flow ratio and the like, the prepared MgO/Al2O3 composite film has higher secondary electron emission coefficients and better e-beam bombardment resistance performance. By adopting the method, the prepared MgO/Al2O3 composite film has the advantages of controlled thickness of the film, uniform components, high secondary electron emission coefficients, excellent e-beam bombardment resistant performance and the like.