Abstract: This paper smdies the relationship between the fusing characteristics of copper wire and the overload current. Based on a physical model, the fusing curve for the copper wire is obtained. According to the space application of the copper wire, the shooting method and the minimum squares error method are used to modift the physical model, an equivalent heat conduction coefficienti k_q obtained to establish the fusing curve. The maximum current density is given for the safe use under both vacuum and atmospheric conditions.