Rapid melting of a subcooled single-component metal powder bed in Selective Laser Sintering (SLS) is analyzed in this paper. Under irradiation of a pulse laser beam, the surface of the powder particle is molten first while the core of the particle remains solid. The temperature of the liquid layer is higher than the melting point, while the temperature of the solid core is below the melting point. Therefore, the mean temperature of the partially molten particle is within a range of temperature adjacent to the melting point. In addition, the powder bed experiences a significant density change during melting because the interstitial gas initially in the pore space is driven out as melting progresses. Melting in SLS of single-component metal powder can therefore be modeled as that occurring in a range of temperature with significant density change. The temperature distributions in the solid, liquid, and mushy zones and locations of the various interfaces are obtained by using an integral approximate method. The effects of initial porosity, dimensionless initial temperature, and dimensionless thermal conductivity of the interstitial gas on the surface temperature and locations of the interfaces are investigated.