The effect of diffusion time on the microstructure and properties of Inconel 718 superalloy transient liquid phase diffusion welded joints were studied by means of mechanical properties test,interface microstructure observation and element distribution analysis under welding temperature of 1100 ℃ and welding pressure of 1 MPa,using BNi2 as intermediate layer. The results show that the extension of diffusion time can make the intermediate layer elements diffuse more fully,weaken the aggregation degree of precipitates in the diffusion region and increase the joining strength of the joint. The shear strength of the joint reaches 511 MPa when the pressure is 1 MPa at 1100 ℃ for 120 min,and when the diffusion time is 120 min,the shear strength of the joint increases by 10.2% compared with 60 min and 22.9%compared with 30 min. The HV of Inconel 718/BNi2 TLP joint shows M-shaped distribution,that is,the HV in diffusion zone is the highest,and that in isothermal solidification zone is the lowest. The HV of base metal is higher than that in the isothermal solidification zone.