According to the demand for inhibiting background of the correlation system, Al, Cr and SiO2 were choosed as the coating materials. Based on the absorption theory, a broad spectrum absorbing film was designed by combining with the film design software, and by using the vacuum deposition technology, the film samples were prepared. The internal stress of the film was reduced by stepped vacuum annealing, and the problem of film adhesion was solved. Using the interactive analysis and reverse inversion methods to analyze the testing results, the thickness of sensitive thin layers was controlled precisely by optimizing the process parameters, as a result, and the thickness control error was reduced. The average absorptivity of prepared absorbing film is 99.1% at the band of 400～1 100 nm, which meets the requirements of the system.