To reduce the seal failure rate of diesel engine crankshaft oil seals，market failure data of a certain platform's diesel engine crankshaft oil seals is statistically analyzed. Using fishbone diagrams，possible causes of oil seal failure and leakage are analyzed from six aspects：human，machine，material，method，environment，and measurement. The root cause of failure is verified through comparative tests of oil seal reliability from different suppliers and oil seal consistency assessment bench tests. On this basis，the improvement measures to reduce the sealing failure rate are proposed and tracked in the market. The results show that the failure rate of oil seals for cement mixer trucks is the highest，and the failure rate of the rear oil seal is significantly higher than that of the front oil seal. The main failure modes of faulty oil seals include main lip line failure，eccentric wear，and felt fuzzing. The main reasons for seal failure are the insufficient of followability of the oil seal and the inadequate density of the rubber material，defective production assembly process，uncoated end caps and gear shaft end faces，and poor assembly performance of combination oil seals. The oil seal parameters are optimized，as well as the injection vulcanization process，gluing on end caps and gear shaft heads，and assembly processes. After improvement，the failure rate of the oil seal market has significantly decreased.