Manual SHS welding is a new method of emergency welding based on SHS reaction. The large amount of Al2O3 created in the reaction restricts the welding performance seriously. In this paper, CaO and MgO were added as slagging elements to improve the characters of the slag, and the effects of their addition have been studied. Results showed that the combustion velocity of the rod decreased when the content of CaO and MgO increased. The rods with 0.2g MgO and 1.2g or 1.5g CaO were easy to control, which combustion velocities were about 12mm•s-1. No obvious changing rule was found for the density of the slag when the content of additives changed. But the densities of slag were all lower than that of metal Fe and Cu. Viscosity calculation showed that the viscosity value of slag increased when the temperature drop. The additive CaO and MgO reduced the slag viscosity. The viscosity value of the slag with 1.5g CaO and 0.2g MgO added was about 0.9 Pa•s at 1450°C and was lower than 0.7 Pa•s at 1500°C. Welding experiments showed the fluidity and the detachability of the slag were improved. Phase composition and microstructure analysis showed that the slag had multi-phases and its matrix was glass. The tensile strength of the joints was above 350MPa, which meets the requirement of mechanical properties for emergency welding. SEM micrograph showed there were slag inclusion in the fracture of welded joint, which was one of the reasons restricting the mechanical performance of the weld joint.