The interaction mechanism between sodium arsenate and fayalite-type copper slag at 1200？°C was investigated through XRD, XPS, HRTEM, TCLP and other technical means and methods. The results indicated that the proportions of sodium arsenate in the slag and flue gas phases were approximately 30% and 70%, respectively. The addition of sodium arsenate depolymerized the fayalite structure and changed it from a crystalline state to an amorphous state. The fayalite structural changes indicated that the [AsO₄] tetrahedron in sodium arsenate combined with the [SiO₄] tetrahedron and [FeO₄] tetrahedron through bridging oxygen to form a silicate glass structure. The TCLP test results of the samples before and after the high temperature reaction of fayalite and sodium arsenate showed that after high temperature reaction, fayalite could effectively reduce the leaching toxicity of sodium arsenate, reducing the leaching concentration of arsenic from 3025.52 to 12.8 mg /L before and after reaction, respectively.