The invention relates to a preparation method of a phenolic emulsifier. The preparation method has advantages of simple synthesis technology, mild reaction condition and high yield, and is easy to realize industrialization. The invention also relates to emulsified bitumen emulsified by the phenolic emulsifier obtained by the above preparation method and an application thereof. The preparation method of the phenolic emulsifier contains the following steps of: performing a reaction between polyamines and aldehyde to generate aldimine, adding alkylphenol, performing a reaction to generate Mannich base, and acquiring the phenolic emulsifier, wherein the mol ratio of alkylphenol to aldehyde to polyamines is 1: (1-1.5): (1-1.5); alkylphenol is a compound as shown in the structural formula II; aldehyde is a compound as shown in the structural formula III; and polyamines is a compound as shown in the structural formula IV. The preparation method has advantages of simple synthesis technology, mild reaction condition and high yield, and is easy to realize industrialization. The emulsifier obtained by the preparation method has good emulsifying property. Each performance of the prepared emulsified bitumen meets the cationic emulsified bitumen standard and agitation performance technical indexes which are set by the Ministry of Communications.