Melting of a subcooled powder bed that contains a mixture of two powders with significantly different melting points was analytically investigated. The effect of density change on the melting process was taken into account in the physical model. The temperature distributions in the liquid and solid phases were, respectively, obtained by an exact solution and an integral approximate solution, while the effect of the unsintered powder porosity on the liquid phase shrinkage during the melting process was investigated. This effect paves the way to simulation of the complication and complex 3-D selective laser sintering (SLS) process.