The invention discloses a brazing material for brazing molybdenum-rhenium alloy, a preparation method and a brazing method. The brazing material comprises, by weight, 17.5%-19.5% of Cr, 6.5%-8.5% of Si, 0-1.5% of B, 0-5% of W and the balance of Ni. The brazing material is high in melting temperature and uniform in melting; a brazing material foil is conducive to promoting element diffusion and interface reaction in the process of connecting the brazing material, solid solution metallurgical reaction of the brazing material and the molybdenum-rhenium alloy is improved, residual stress in a brazing joint is reduced, content of embrittled substance in the brazing joint is lowered, and mechanical performance of the joint is improved. The preparation method of the brazing material is simple, convenient, practical, supportive of repeating and reproducing and convenient for popularization and application. By adopting the brazing method, through vacuum brazing connection, a weldment when being heated is in a vacuum state and is free of deformation and grain coarsening, oxidation and pollution are avoided.