Abstract: A 51CrMnVA leaf spring of heavy duty truck broke when placed in winter after being preloaded. The early fracture reasons were analyzed by fracture analysis, microstructure observation, mechanical performance testing, and comparison with the fractured leaf spring after normal service. The results show that the high strength and hardness and low toughness of the leat spring due to a relatively low tempering temperature, and high diffusible hydrogen content in steel and high tension rates during presetting caused the brittle fracture of the leaf spring at low temperatures. Reducing the diffusible hydrogen content in steel, increasing the tempering temperature, extending the tempering time, increasing the number of hydrogen traps, and achieving appropriate matching of strength and toughness could effectively avoid early failure and hydrogen-induced delayed fracture of the leaf spring.