The invention discloses a preparation method of an MDI-based polyurethane slow-elastomer. The preparation method includes following steps: (1) preparing polyester, polyether, polycaprolactone or polycarbonate-blocked polysiloxane dihydric alcohol; (2) preparing a pre-polymer; (3) preparing a chain extender and (4) performing a pouring process and a post-aging process. By means of addition of an organic silicon component, the MDI-based polyurethane slow-elastomer material is not only greatly enhanced in high-temperature resistance but also is improved in hydrolysis resistance. In addition, the material is greatly reduced in noise when being used. The material is significantly enhanced in use performance under a situation of high temperature and high humidity, is broadened in use application range and can reduce noise pollution.