The invention relates to the field of plastic pipe processing, in particular to a high-density polyethylene and PET alloy pipe and a preparation method thereof. The composition formula of the alloy pipe by weight includes 100 parts of PE100 and 20-50 parts of PET, corresponding to 5-8 parts of compatibilizer, 10-25 parts of reinforcing agent, 0.2-1.0 parts of processing aid, 0.8-1.5 parts of concentrated color masterbatch; at the same time, its preparation method is disclosed, which is to carry out compatibilization and blending of PET and high-density polyethylene Modification, and according to the above-mentioned scientific component formula, high-density polyethylene and PET alloy pipes are obtained by weighing raw materials, kneading technology, extrusion molding and other processes, thereby improving the strength, modulus, surface hardness, and durability of pipe products. Heat resistance, wear resistance and fatigue resistance make pipeline products more suitable for fields such as trenchless technology, broaden the application occasions of pipeline products, and reduce and eliminate the occurrence of quality accidents.