An injectable soy protein isolate and a preparation method thereof belong to the technical field of soy proteins and processing. The preparation method comprises the following steps: using low temperature soy meal as the raw material, preparing milk curds of the protein isolate by carrying out alkali extraction, degasification and acid precipitation on the raw material, then using neutral proteinases to carry out enzymolysis on the milk curds of the protein isolate, carrying out thermal enzyme inactivation, sterilization, flash evaporation, homogenization and spray drying after reaction and finally spraying aqueous solution or liquid hydroxylated modified soy phospholipids of powdered soy phospholipids, soy lecithin or powdered hydroxylated modified soy phospholipids on the dry powder obtained by spray drying to obtain the soy protein with good dispersibility, water absorptivity, water-retaining property, oil absorption property and gel property. The soy protein isolate can be used insuch industries as injectable meat products, low temperature meat products, solid beverages, flour products and condiments, etc.