The invention relates to a preparation method for an embedding floating bacteria agent of nutritive salt, expandable graphite and microorganism together. The preparation method for the embedding floating bacteria agent of the nutritive salt, the expandable graphite and the microorganism together comprises the steps of using a sodium alginate solution as an embedding frame, adding a nutritive salt solution, the expandable graphite and petroleum degrading bacteria to the sodium alginate solution, mixing evenly, dripping into a calcium chloride solution to embed, crosslinking for the night under the condition of 4 DEG C, and obtaining an embedding bacteria agent capable of strengthening bioremediation effect. The bacteria agent prepared by the preparation method for the embedding floating bacteria agent of the nutritive salt, the expandable graphite and the microorganism together is suitable for in-situ remediation of marine petroleum pollution, and has the advantages of being long in floating time, good in mass transfer performance, high in petroleum degrading efficiency, and the like. The method that the nutritive salt and bacteria solutions are embedded together is adopted by the embedding bacteria agent, defects that nutrition of marine environment is poor and additionally the nutritive salt is diluted quickly are overcome, and floating of the bacteria agent is achieved by addition of the expandable graphite. When the embedded bacteria agent is used, the embedded bacteria agent can be directly added to the surface of a polluted water body, effective contact with petroleum pollutant is ensured, biodegradation efficiency is effectively improved, and recycling is facilitated, and risk of a secondary pollution does not exist.