The invention discloses a preparation method of an amide asphalt emulsifier, which comprises the following steps: uniformly mixing a water carrying agent, a metal ion compound, carboxylic acid and polyethylene polyamine to form a reaction system, carrying out reflux reaction at a temperature of 80-100 DEG C, carrying out pressure reduction and distillation and removing the water carrying agent to prepare the amide asphalt emulsifier, wherein the metal ion compound is a catalyst, and the molar ratio of the carboxylic acid to the polyethylene polyamine is (1:10)-(10:1). Through the preparation method, the amide asphalt emulsifier can be synthesized at a lower temperature. Compared with the conventional chemical synthesis method, the preparation method has the advantages of simplicity and convenience in operation, mild reaction condition, environment friendless and the like.