Abstract: The microstructure, mechanical property and susceptibility to hydrogen embrittlement of a low-carbon and low-alloy steel treated by quenching-partitioning-tempering (Q-P-T) process was studied, and compared with those of the steel treated by traditional quenching-tempering (Q-T) process. The results show that the steel treated by Q-P-T process contained more retained austenite, the ductility and toughness increased by 3.5% and 27% respectively, and the susceptibility to hydrogen embrittlement decreased comparing with that by Q-T process. The retained austenite plays a positive role in decreasing the susceptibility to hydrogen embrittlement.