The invention relates to a chlorine-containing high-performance heterocyclic aromatic polyamide fiber and a preparation method thereof, belonging to the field of organic fiber materials and aiming atsolving the problem that thermal stability and flame retardance of existing heterocycle aramid fibers need to be improved. The preparation method comprises the following steps: firstly, adding p-phenylenediamine, 2-(4-aminophenyl)-5-aminobenzimidazole, chlorine-containing p-phenylenediamine and 2,2'-butylidene bis[5-aminobenzoxazole] into a reaction kettle filled with a mixed solvent, completely dissolving, then lowering temperature in the reaction kettle to the temperature ranging from -10 DEG C to 10 DEG C, adding paraphthaloyl chloride, reacting for 0.5-2 hours, then heating to the temperature of 60-90 DEG C, and reacting for 2-5 hours, thus obtaining chlorine-containing heterocyclic aromatic polyamide; and secondly, defoaming and carrying out wet spinning. The chlorine-containing high-performance heterocyclic aromatic polyamide fiber provided by the invention has the advantages that a heterocycle is introduced onto a macromolecular main chain and oxygen is contained in a lateral group, so that the surface activity of the fiber is improved, breaking strength reaches 3.50-5.0GPa, and limit oxygen index is 30-50%.