In order to improve the sound absorption performance of the sound absorbing material in water, impedance gradient underwater sound absorbing composite with multiphase (IGCM) is prepared in this study. By superposing several layer materials of different impedance gradients, the mixture is poured in the mold layer by layer so that three kinds of IGCM with different mass density gradients of iron powder, tungsten powder and mixture of iron powder and tungsten powder are prepared. Under two operating conditions of the incident angle of 0°and 20°, the results show that the three IGCMs have good broadband absorption characteristics. The sound absorption frequency ranges of the three samples of IGCM under normal incident conditions are concentrated between 6kHz and 10kHz. The sound absorption performance of IGCM under oblique incidence is better than that under normal incidence, especially the IGCM with iron-tungsten powder, which could achieve wide-band strong sound absorption from 2kHz to 10kHz under the condition of oblique incident. The IGCM with iron-tungsten phase under sound wave's incident angle of 20 ° exhibits better sound absorption performance than the other two, which provides a theoretical reference for the design and manufacture of gradient sound absorbing materials.