The invention relates to preparation technologies of a chemical product, and particularly to preparation technologies of double-acid-single-alcohol copolymerization modification PET-A and a unidirectional heat shrinkable film thereof. A preparation method of the double-acid-single-alcohol copolymerization modification PET-A comprises adopting pure terephthalic acid (PTA), isophtalic acid (IPA), and mono ethylene glycol (MEG) as main raw materials and acquiring PET-A by carrying out ternary polymerization modification on the raw materials. The preparation technologies of the unidirectional heat shrinkable film of the double-acid-single-alcohol copolymerization modification PET-A comprises two types of preparation technologies, and one is vertical and the other is horizontal. Heat shrinkable films prepared by adopting the two types of preparation technologies have the same performance. The preparation technologies of the invention have the advantages of easy availability of raw materials, simple and environmental protecting preparation technology, high transparency of products, and broad applications. The preparation technologies of the unidirectional heat shrinkable film provided by the invention are specially used for preparing food packaging heat shrinkable film materials. Finished products obtained by drawing the products vertically or horizontally have good transparency and heat shrinkage rate of the finished products reaches 45-80% within 2-3s at a temperature of 95-130DEG C. The unidirectional heat shrinkable film of the invention can replace poisonous PVC heat shrinkable food packaging bags and other series of heat shrinkable packaging materials.