The invention relates to an application of a scandium-containing rare earth catalyst in catalysis of aromatic amine para-selective alkylation reaction. The structural formula of the scandium-containing rare earth catalyst is shown in the specification. The aromatic amine is aromatic primary amine or aromatic secondary amine. The invention also discloses a preparation method of the para-alkylated aromatic amine. The preparation method comprises the following steps: performing a reaction on aromatic amine shown in the formula (1) and olefin shown in the formula (2) in an organic solvent at 60-150 DEG C under the catalytic action of a scandium-containing rare earth catalyst to obtain the para-alkylated aromatic amine, the reaction route being represented as the specification; wherein R1 is hydrogen, an aryl group or a C1-C10 alkyl group; R2 is hydrogen, C1-C4 alkyl group, C1-C4 alkoxy group, aryl group or halogen and cannot be substituted at a para-position; X is methylene or sulfur atom,and n1 is any one of 0 to 4; R3 is C1-C20 alkyl group, aryl group or cyclized with R5 through a plurality of methylene groups, and the number n2 of the methylene groups is any one of 1 to 4; R4 is hydrogen, C1-C20 alkyl group, aryl group, thienyl group, benzofuryl group or substituted aryl group; R5 is hydrogen, methyl or methylene; R6 is hydrogen.