Abstract: Contact reactive brazing(CRB) is often used in joining of all kinds of materials.Taking the example of brazing LF21 Aluminum alloy using Si as interlayer,the mechanical responding process of contact reactive brazed joint with different seam thickness to tensile load was analyzed to gain proper thickness of the interlayer by means of finite element numerical simulation.The calculating results showed that the maximum level of tensile stress of the joint responding to the load is lied at the interface of the brazed seam and the base metal,more over,there is a liner relationship between the maximum stress and the load.Namely,the substance of joint's responding to tensile load is linear enlarging for it.So the mechanical responding factor of the brazed joint was put forward in the paper,which increases with the increasing of the thickness of the brazed seam,and results in the decreasing of the tensile properties of the joint.The simulation mentioned above was confirmed by series experiments,and the proper thickness of the brazed seam is 50~80 μm for the CRB joint of Al with Si as an interlayer.The thickness range of Si interlayer,6.6~10.0 μm, was gained based on the Al-Si binary system.