Two-dimensional (2D) ferromagnets with high Curie temperature have long been the pursuit for electronic and spintronic applications.CrI3 is a rising star of intrinsic 2D ferromagnets,however,it suffers from weak exchange coupling.Here we propose a general strategy of self-intercalation to achieve enhanced ferromagnetism in bilayer CrI3.We show that filling either Cr or I atoms into the van der Waals gap of stacked and twisted CrI3 bilayers can induce the double exchange effect and significantly strengthen the interlayer ferromagnetic coupling.According to our first-principles calculations,the intercalated native atoms act as covalent bridge between two CrI3 layers and lead to discrepant oxidation states for the Cr atoms.These theoretical results offer a facile route to achieve high-Curie-temperature 2D magnets for device implementation.