The invention relates to a preparation method of a high-performance room temperature complex-phase magnetic cooling material. The complex-phase magnetic cooling material comprises amorphous ferrous alloy and crystalline rare earth based alloy. The preparation method comprises the following steps of: (1) preparing the amorphous ferrous alloy by adopting a melt-spun process, mechanically crushing and then carrying out ball milling to prepare powder; (2) preparing the crystalline rare earth based alloy by adopting an ingot casting process, a fast-hardening and strip-casting process or a melt-spun process, mechanically crushing after heat treatment, and then carrying out ball milling to prepare powder; or preparing alloy powder by directly adopting a mechanical alloying process; (3) evenly mixing the amorphous ferrous alloy powder and the crystalline rare earth based alloy powder in the protection atmosphere or vacuum; (4) carrying out compression molding on mixed powder in the protection atmosphere or vacuum; and (5) preparing a pressed blank into amorphous/crystalline complex-phase blocky alloy by adopting a rapid sintering process below the crystallization temperature and in the protection atmosphere or vacuum. The prepared complex-phase magnetic cooling material has high magneto-thermal performance, high decay resistance performance, low hysteresis lag and cost and simple process, and is suitable for large-scale batch production.