The invention belongs to the field of food nutrition, and particularly relates to a one-step self-assembly preparation method of succinylated casein-phospholipid-anthocyanin nanoparticles and application of the nanoparticles in gastrointestinal tract sustained release. By adjusting a prescription process, succinylated casein, phospholipid and anthocyanin are simply and efficiently mixed by adopting a one-step self-assembly method to prepare the nanoparticles, and the specific method comprises the following steps of dissolving quantitative anthocyanin with HCl, adding a phospholipid solution, stirring in a water bath, adding a succinylated casein (ultrapure water) solution, stirring in a water bath again, fully mixing the two solutions, and obtaining the target anthocyanin nanoparticles, wherein the particle size of the anthocyanin nanoparticles is 70-100 nm (PDI is 0.10-0.15), the encapsulation efficiency is 40-70%, and the drug loading capacity is 5-20%. The one-step self-assembly method for preparing the anthocyanin nanoparticles is simple and rapid, later industrialization is easy, slow-release absorption of the anthocyanin can be remarkably improved, and the bioavailability of the anthocyanin is greatly improved.