Abstract: Using tapioca starch as raw material, starch nanoparticles were prepared by ultrasonic stirring, and characterized by scanning electron microscopy, laser nanoparticle sizer, and X-ray diffraction. In the sedimentation stage of starch nanoparticles, kaempferol solution was used as the non-solvent phase with 0.7 mg/mL kaempferol solution to simultaneously embed kaempferol to prepare kaempferol starch nanoparticles. The influence of ethanol concentration on the embedding rate of kaempferol was explored, and the release rate and stability of kaempferol after embedding were investigated. The results showed that when the ethanol concentration was 60%, starch nanoparticles were formed, and the size was uniformly distributed between 50 and 200 nm, when the ethanol concentration was less than 40%, V-shaped starch particles were formed. When the ethanol concentration was 30%, the entrapment rate of kaempferol was the highest, at 62.94%, and the embedding amount was 3.78 mg/g. In a simulated body fluid environment, the kaempferol starch nanoparticles can continuously release the drug for 20 h. The release rate was 88.75%, while the original kaempferol was almost completely released in 3 h, the release rate was 93.75%, and the release rate increased with the increasing of the ethanol concentration of the sustained-release medium. Compared with the aqueous solution of kaempferol, the retention rate of kaempferol increased from 43.17% to 75% when the kaempferol starch nanoparticles were allowed to stand at room temperature for 5 h, which had a stable embedding effect. It could be seen that the simultaneous embedding preparation technology would have a good embedding slow-release effect and stabilizing effect on kaempferol.