The invention relates to a method for separating N-beta-hydroxyethylethylene diamine from a piperazine byproduct. The piperazine byproduct is produced through catalyzing, dehydrating, cyclizing and synthesizing the N-beta-hydroxyethylethylene diamine; the method comprises the following steps: in a splitting solution, the piperazine byproduct and sufficient acid fully react at a temperature of between 50 and 80 DEG C; after reaction is completed, the reaction solution is cooled at a temperature of between 0 and 30 DEG C, is precipitated with a compound crystal and is filtered; a filter cake A is taken out, is added with a recrystallization solvent, is recrystallized and is filtered; a filter cake B is taken out, is hydrolyzed through 2 to 10 percent hydrochloric acid, is kept stand and is delaminated; an organic layer is taken out, washed and dried to obtain the monomer N-beta-hydroxyethylethylene diamine; the acid is one of formic acid, acetic acid, oxalic acid, phenylsulfonic acid, hydrochloric acid, phosphoric acid or hydrobromic acid; the splitting solution and the recrystallization solvent are selected from methanol, ethanol and water respectively. The method has high splitting efficiency; the yield of the monomer N-beta-hydroxyethylethylene diamine is between 80 and 95 percent; and the purity of the monomer N-beta-hydroxyethylethylene diamine is between 93 and 99 percent.The method has low implementation cost, has a simple reclaiming method and high reclaiming rate of the used acid and saves cost.