The invention relates to a method for preparing an yttrium silicate coat by cathode rotation hydrothermal electrophoretic deposition. A cathode rotation hydrothermal electrophoretic deposition method is used for preparing an yttrium silicate antioxidant coat on the surface of carbon/carbon-carborundum composite. Yttrium silicate powder is used as raw material to be respectively made into the yttrium silicate coats with compact structure, microcrack and different thickness in certain powder material proportion, under certain temperature and voltage and at different cathode rotation speeds. Themethod has the advantages of simple technical control and uniform coat, avoids repeated operation to certain extent and can be used for product with complex surface, and the method can obtain the yttrium silicate coat with controllable structure and good performance under low temperature.