Computational thermodynamics and kinetics were used to design the Pb-free micro-solders for replacing the conventional Sn-Pb solders because of the health and environmental safety problem.On the basis of CALPHAD (Calculation of Phase Diagrams) method we can easily calculate properties such as the liquidus projection, isothermal and vertical sectional diagrams and phase fraction in multicomponent system including Ag, Bi, Cu, In, Sb, Sn, Zn and Pb elements. Inaddition, other related information such as the surface tension, viscosity of the liquid phase and solidification simulation can also be obtained. DICTRA (Diffusion Controlled Transformation) software was used to simulate the interfacial reactions between substrate and Pb-free solders, which can easily give the information on the growth of intermetallic compounds and moving speed of interface between substrate and solders etc.