Brittle intermetallic compounds in brazing joint of Titanium and steel easily make its weld organization and mechanical properties worsen. In order to solve this problem, we do a series of contrast test that the Ni layer is plated on matching surface of base metal or not. On this basis, the influencing mechanism of atomic diffusion behavior, microstructure and mechanical properties of the brazing joint were researched. The test results show that, the Ni layer blocks the atoms diffusion of brazing joint. Moreover, the degree of obstruction are differences among Fe,Ti and other atoms. Further, this differential is in close relationship with physical location of Ni layer in the joint region. The hinder of Ni layer alters osmotic concentration of the atoms, slows the metallurgical reaction degree, and reduces the content of brittle intermetallic compounds .Consequently, the microstructure and mechanical properties of brazing joint can be effectively improved because of the existence of Ni layer.