Abstract: Oil pressure of АЛ-31Φ engines was often found to be lower during service. Russia did not work to improve the oil system from the design principle, resulting in such frequent failure. Combined with working principles of the oil systems in domestic and international third-generation aircraft engines, the gear of oil booster pump was widened and the gear chamber of the shell were improved. These measures not only guaranteed the strength requirement of the oil parts and increased the oil flow by 12%. The failure of lower oil pressure was solved from the design principle and the reliability of the engines was enhanced.