In order to solve the imbalance between strength and toughness in different cross sections of a large size piston for hydraulic crushing hammer, the influence of heat treatment and microstructural adjustmen/control on the microstructure and mechanical properties of 9CrV steel near-real shaped piston with a diameter of 190 mm was studied. The results show that when the piston were austenitized at 850℃ for 5 h and quenched at 230℃ for 4 h, then tempered at 230℃ for 4 h, the microstructure of a piston consists of bainite, bainite + troostite + residual austenite and pearlite respectively, from the surface to the core. The tensile strength of the piston surface layer is 1442 MPa, the impact absorbed energy is 11 J, the impact toughness in the piston core part is poor, and the impact toughness is the lowest at 2/3 R of the piston. When the austenitizing temperature is decreased to 800℃ and tempering temperature is increased to 400℃, the tensile strength of the piston surface layer increased to 1610 MPa, and the impact absorbed energy decreased to 7.4 J. The impact toughness of the piston core shows an increasing tendency, while the strength will decrease. When the piston is austenitized at 800℃ for 5 h and followed by quenching at 230℃ for 4 h, then tempering first at 230℃ for 4 h and then at 400℃ for 4 h, the tensile strength of the piston surface layer becomes 1672 MPa, the impact absorbed energy becomes 9.8 J. The impact toughness of piston core part has been improved, and the combination of strength and toughness of the piston tend to balance. It is found that with the lower austenitizing temperature a large number of undissolved carbide particles will be retained, it will hinder austenite growing, but refine grains. With the increasing tempering temperature, the dislocation tangles to pearlite ferrite will be restored, and the toughness of piston core can be improved. The carbon-rich residual austenite film in the bainite of piston surface layer is stable. When it is tempered at 400℃, the carbide thin film will precipitate during the decomposition of residual austenite, which is easy to become a rapid crack propagation path and reduce the impact toughness. The residual austenite was transformed into lower bainite by tempering at 230℃ to prevent the formation of thin-film carbides by tempered at 400℃ to improve the impact resistance of piston core, so that the toughness becomes balance in the different cross section parts of a piston. Based on the combination of optimizing and controlling of piston microstructure and heat treatment process, the strength and toughness of the piston are balanced.