Abstract: In this paper, a broadband absorber based on indium tin oxide (ITO) thin film is designed, which can achieves more than 90% absorption between 1.92 GHz to 13.15 GHz. Absolute bandwidth is 11.12 GHz, and relative bandwidth reaches 149.04%, completely covering the S, C, X band, partly covering L band and Ku band, and achieve a peak absorption rate of over 99%. Firstly, BP neural network is used to calculate the equivalent impedance of the surface structure composed of square ring and square patch. Secondly, the effects of different layers are simulated and optimized by genetic algorithm. Finally, based on the equivalent transmission line theory, the reflectivity of the optimized unit is expressed analytically and compared with the simulation results. The simulation and test results show that the absorption curve of the element changes little under different polarization and different oblique incidence angles, indicating that the structure has the characteristics of polarization insensitivity and large incidence Angle. The method proposed in this paper solves the problem that the traditional empirical formula is not universal to the structural parameters. Since ITO is used as the surface structure, the real part of its impedance can be adjusted in a wide range. The absorbing body of any wave band can be designed quickly and accurately without sweeping parameters in theory.