The invention discloses a preparation method and application of a porous easy-to-disperse multifunctional composite rubber additive, and belongs to the field of rubber additives. The method comprisesthe following steps: adding an MBT intermediate product in a process of synthesizing MBT from aniline by a high-temperature and high-pressure method into a pressurizing tank, heating, introducing carbon dioxide, regulating the pressure in a pressurizing tank to 72.9 atm or above, keeping the temperature and the pressure for a certain period of time after a molten material reaches a balanced state,transferring out the material, condensing and granulating. According to the preparation method, supercritical carbon dioxide is used for preparing the porous easily-dispersed multifunctional composite rubber additive, the obtained product forms a foam structure on the microscopic level and is more easily dispersed in a rubber compound matrix in the processing process, and the dispersity of the product in the rubber matrix and the poor scorching resistance of the rubber compound can be obviously improved. In addition, the porous easily-dispersed multifunctional composite rubber additive obtained by the method is used as a rubber additive, so that the mechanical property of rubber can be obviously improved.