After altering ground tire rubber(GTR) with formic acid and hydrogen peroxide, the epoxidation product (EGTR) was produced. The poly(lactic acid) (PLA)/EGTR blends were then made using the melt blending method, and their micro-morphology, crystalline behavior, and mechanical properties were all carefully examined. The results showed that the carbon-carbon double bond on the GTR molecular chain was successfully oxidized to an epoxy group by formic acid and hydrogen peroxide. The EGTR particles were evenly distributed throughout the PLA matrix, demonstrating good compatibility between the two phases. Furthermore, low levels of EGTR promote PLA crystallization, while high levels of EGTR inhibit PLA crystallization. The PLA/5% EGTR blends had the highest crystallinity of 11.1%, which was 4.8 times higher than that of pure PLA. The blends tensile strength declined as the EGTR content increased, while the impact strength and elongation at break showed a tendency of first increasing and then decreasing. When 10% EGTR was added, the blends had the maximum elongation at break and impact strength, with good toughening effect and tensile strength, showing the best overall mechanical properties. The study provides a basis and technical foundation for modifying PLA with GTR as a toughening material and promotes the recycling of waste rubber.