The invention discloses a rare earths-containing iron-based solder for stainless steel braze welding and a method for braze welding by using the solder, and relates to a rare earths-containing iron-based solder and a method for braze welding by using the solder. The invention aims to solve the problems of the existing iron-based solder that the melting temperature is high, phosphorus brittle phase is caused when the existing iron-based solder is used for welding, and the shearing strength of a joint is greatly lowered. The rare earths-containing iron-based solder for stainless steel braze welding is prepared from Cr, Ni, Si, P, Cu, rare earths of the lanthanide series and Fe according to the mass fraction. Powder of the Fe, Cr, Ni, Cu, P, Si and rare earths of the lanthanide series is heated so as to reach a liquid alloy state, an atomization method is adopted for obtaining alloy powder, the powder and a binder are uniformly mixed, and are coated on a to-be-welded surface of stainless steel, a workpiece to be welded is obtained, the workpiece is put into a vacuum braze welding furnace, and then vacuum braze welding treatment is carried out. The solder and the method have the advantages that the shearing strength of a welding joint can reach 180-200Mpa, and excellent mechanical property can be realized.