The flavor is a decisive sensory characteristic that determines the popularity of French fries (FFs). During high-oleic rapeseed oil (RO) frying, the flavor development of FFs showed three noticeable stages including break-in (3%-8.0% of total polar compounds (TPC)), optimum (8.0%-20% of TPC), and degrading stages (above 22% of TPC). In order to distinguish the key aroma compounds in each stage, the FFs prepared in RO at TPC of 3% (FF1), 10.5% (FF2), and 27% (FF3) and their relevant oils (RO1, RO2, RO3) were selected for sensory-directed analysis. The results revealed that the FF1 had low contents of (E,E)-2,4- decadienal (deep-fried odor) which could be the reason why FF1 samples were rated with low-sensory score. The FF3 had higher hexanoic acid (sweaty odor), heptanoic acid, nonanoic acid, benzene acetaldehyde (stale odor), and trans-4,5-Epoxy-(E)-2-decenal (metallic odor) compared with FF1 and FF2, which resulted in flavor deterioration in FF3. Moreover, the decrease of 2,5-dimethylpyrazine and 2-ethyl-6-methyl-pyrazine in FF3 induced the lower roast flavor, which may also lead to the decline of the sensory score. Similarly, the higher portion of (E)-2-undecenal, hexanoic acid, heptanoic acid, and nonanoic acid in RO3 leads to increase in its rancid score and thus lower the sensory score. When the TPC content exceeded 22%, the peroxidation of the oil could cause the rancid taste. Therefore, it should be controlled in the later stage of frying. By understanding the changes of key flavor substances during the frying process, it can be significantly used as a reference for the development of fried products with the best flavor.