The invention relates to a preparation method for utilizing geothermal water to build a super hydrophobic layer on the surface of bamboo or wood. The preparation method comprises the steps of firstly,carrying out treatment by using a NaOH solution to remove lignin on the surface of the bamboo or wood so as to expose hydroxyl on the surface layer as much as possible, then soaking the bamboo or wood into a glycidyl methacrylate solution for reaction, and at last depositing calcium carbonate crystals on the surface of the bamboo or wood by using a hydrothermal method, wherein an aragonite type calcium carbonate surface layer is built on the surface of the bamboo or wood by combining the calcium carbonate crystals and polydimethylsiloxane as a low surface energy material. The preparation method for utilizing the geothermal water to build the super hydrophobic layer on the surface of bamboo or wood has the advantages that because of carrying out treatment by using the NaOH solution to remove the lignin on the surface of the bamboo or wood so as to expose hydroxyl on the surface layer as much as possible, it is beneficial for the reaction of the next step; GMA is used as a coupling agent, epoxy groups react with hydroxyl to make GMA fixed to the surface of bamboo or wood, carboxy groups and Ca2+ form complex, the growth crystal type and morphology of calcium carbonate are controlledby adjusting the complex formed by the carboxy groups and the Ca2+; and the preparation method is friendly to the environment, good in biological compatibility, low in production cost and good in hydrophobic property.