Abstract: In this paper,microstructure analysis and mechanical properties tests were carried out on 10Ni5CrMoV steel with thickness 100mm,which is trial-produced with existing element ingredient.The results indicate that the steel is hardenable at total thickness of 100mm.After quenched and tempered,fine and uniform martensite and bainite is observed.The property of the sample fabricated from different thick part of the thick plate meets the requirement,and good matching of high strength and high toughness can be obtained.The results showed that existing element ingredient of 10Ni5CrMoV steel can be applied in production of thick plate.