A high-efficiency air-entrainer for roller compacted concrete and a preparation method thereof are disclosed. The air-entrainer is prepared from the following raw materials (by weight): 22-25 parts of1,4-dibromobutane, 43-58 parts of long-chain alkyl primary amine, 16-18 parts of formaldehyde, 13-17 parts of formic acid, 38-42 parts of sodium 3-chloro-2-hydroxy propanesulfate, 20-30 parts of deionized water, 100-110 parts of anhydrous ethanol, and a sodium hydroxide solution. The long-chain alkyl primary amine is one or two of dodecanamine, tetradecyl primary alkane and hexadecyl primary amine. The invention also provides a preparation method of the air-entrainer. The air-entrainer of the invention has a good molecular structure, is endowed with lower surface tension, lower critical micelle concentration and good foam performance and foam stability in comparison with a common concrete air-entrainer, especially has advantages of low dosage and high gas content for roller compacted concrete with low cubic water consumption, and can be applied to water conservancy and water-power engineering. The air-entrainer of the invention has high air-entraining efficiency, good foam stability,low dosage and good dissolvability, is convenient to use, and is economical and practical.