The invention discloses a composite electrolyte for preparing a corrosion-resistant surface of a petroleum pipeline and a preparation method of the corrosion-resistant layer of the petroleum pipelinethrough ultrasonic-assisted electrodeposition, and belongs to the technical field of electrolysis or electrophoresis processes. The electrolyte per liter is prepared from solute raw material components of 150-200 g of nickel sulfate, 50-80 g of nickel chloride, 30-60 g of sodium hydrogen phosphate, 0.1-0.2 g of sodium dodecyl sulfate, 6 g of nano silicon carbide, 10-30 g of sodium sulfate and 30-50 g of citric acid, and the solvent is deionized water. In an electrodeposition process, the nickel and phosphorus in the electrolyte are subjected to a reduction reaction on a stainless steel substrate as a negative electrode to be co-deposited on the stainless steel substrate to form a nickel-phosphorus alloy with an amorphous structure and a smooth surface, and therefore the corrosion resistance of the coating is improved; since the nano silicon carbide is inlaid in the nickel-phosphorus alloy, on the one hand, the nano silicon carbide forms a micro-nano double-roughness structure with thenickel-phosphorus alloy, and forms an air layer between the nano silicon carbide and water drops when making contact with the water drops, so that a hydrophobic structure is formed, and the corrosionresistance is improved; and on the other hand, the wear resistance of the coating is improved, and the service life of the coating is prolonged.