The invention discloses a solder for brazing molybdenum-rhenium alloy foil. The solder comprises the following elements in percentage by weight: 16%-26% of Mn, 6%-9% of Si, 2%-6% of Cu, 0%-3% of Zr and the balance of Ni. The solder is prepared via the following three steps: preparing materials and keeping raw materials pure; and performing vacuum melting to form homogeneous alloy; performing high vacuum melt-spinning so as to prepare the solder into foil with a certain thickness. The brazing temperature of the solder is 1020-1100 DEG C, and the melting temperature of the solder is high, so that the high temperature property of a weldment is guaranteed, and meanwhile, the solder is uniformly melted; the added Zr element can improve the tensile strength of the Ni-based solder; Zr can be used as an inoculant, and can refine grains and improve the structure property, so that the properties of the solder and brazing seams are improved, the diffusion and interface reaction of alloy elements in a brazing connecting process are promoted, the wetting and spreading ability of the solder on the surface of the molybdenum-rhenium alloy is improved, the residual stress is reduced, and the mechanical property of a welding point is improved.