Full-potential linearized augmented plane wave method and Boltzmann transport properties have been used to investigate the crystal structure and electronic structure of Mg2Si. Electronic conductivity, Seebeck coefficient and power factor are calculated. Energy band structure shows that Mg2Si is an indirect semiconductor with energy band gap of about 020 eV. Transport properties versus the doping level have been calculated for the n type and p type doped materials at 700 K. The optimal carrier concentration corresponding to the maxima of power factor are obtained, which are 7749×1019 cm-3 and 1346×1020 cm-3 for the p-doping and n-doping respectively. Maximum ZT value of 093 has been estimated in combination with experimental data of thermal conductivity. From the transport properties at different temperatures, we found that the ratio of power factor to relaxation time is enhanced when the temperature increases. Optimum doping level of materials used in middle and high temperature range is higher than that of materials used in low temperature.