The Mg content in Mg₂(Sn, Si) films obtained by PVD method often deviates its stoichiometric composition due to the easy evaporation of Mg in low pressure. In order to control the Mg content in Mg₂(Sn, Si) lattice and achieve enhancements in thermoelectric efficiency, The Mg-Sn-Si-Bi thin films were deposited on single Si(111) substrate using a Mg-Sn-Si-Bi alloy target and a high pure Mg target by magnetron sputtering alternately. The results show that the Mg content greatly increases, while contents of both Sn and Si decrease in the films with the increasing sputtering time of the Mg target. The thin films possess single cubic Mg₂(Sn, Si) solution phase as the Mg content (atomic fraction) is in the range from 71.437% to 64.497%, the Mg₂(Sn, Si) solution phase disappear and both of Mg₂Sn and Mg₂Si phases occur as the Mg content decreases below 59.813% in the films. Furthermore, the Mg₂Sn phase decomposes and metal Sn occurs as the Mg content in the films decreases to 54.006%. The metal Sn content increases and the Mg₂Sn phase content decreases with the decreasing Mg content in the films, accompanying the near invariable Mg₂Sn phase content. XPS spectrum data show that Mg exhibits the tendency to lose electrons. However, the Sn, Si and Bi exhibit the tendency to obtain electrons in deposited films. It is indicated that the Mg-Sn-Si-Bi thin film with single cubic solution phase possesses higher conductivity due to its higher carrier concentration and higher mobility. The mobility greatly decreases due to the occurrence of metal Sn in the films, thus the conductivity of the films greatly decreases.