Abstract: To address the issues of severe quenching distortion and high post-processing costs commonly encountered in the conventional oil quenching process after vacuum carburizing of AISI 9310 steel internal splines for aviation transmissions, an improved process using high-pressure gas quenching (HPGQ) as a substitute for oil quenching was proposed in this study. Comparative experiments were conducted to systematically investigate the effects of the two quenching methods on distortion, case microstructure, hardness, and tribological properties of the internal splines. It was shown that the profile and lead distortions of the internal splines were reduced by approximately 48%-59% with HPGQ, indicating a significant alleviation of heat treatment distortion. Meanwhile, the case microstructure after gas quenching remained fine acicular martensite with dispersed carbides, with a surface hardness exceeding 61 HRC, and the effective case depth was found to be comparable to that of the oil‑quenched specimens. Friction and wear tests revealed no significant differences in friction coefficient or wear volume between the two processes, both exhibiting excellent wear resistance. Under the premise of maintaining the core case properties, the distortion issue associated with the heat treatment of internal splines was effectively resolved by HPGQ, demonstrating substantial engineering application value.