The aim of this study was to investigate the effects of different numbers of oil recirculation cycles (0, 5, 10, 15 and 20) on the levels of four heterocyclic amines (HAAs) and their precursors, as well as the degree of fat and protein oxidation, in crispy duck legs. The results showed that the levels of four ACS-type HAAs increased with the number of oil circulation cycles, with norharman showing the greatest increase, rising from 0.45 ng/g to 21.60 ng/g, while L-tryptophan, as its primary precursor, increased by 79.11% after the oil been reused 20 times. Regarding lipid oxidation, both the peroxide value (POV) and thiobarbituric acid (TBARS) increased with the number of oil circulation cycles. In terms of protein oxidation, after the oil been reused 20 times, the carbonyl content and protein hydrolysis index (PI) increased significantly, while the total sulfhydryl content (T-SH) decreased significantly. Furthermore, electrophoresis results indicated that oil recirculation accelerates the breakdown of macromolecular proteins into smaller protein fragments, demonstrating that oil recirculation accelerates the oxidative degradation of proteins. Consequently, the reuse of oil leads to the deterioration of fats and proteins, causing the accumulation of heterocyclic amine precursors, and the production of greater quantities of heterocyclic amines. Therefore, the reuse of oil should be avoided as much as possible in production; this provides a scientific basis for the green production of crispy duck legs.