Abstract: MgB₂ powder was successfully synthesized by a self-propagating high-temperature method. Thermodynamic calculation and XRD analysis were used to investigate the powder's synthesizing order and transforming relationship between different Mg-B phases. Phase composition and decomposition temperature in the synthesis process were discussed. The results show that MgB₂ phase has synthesized without other impurities such as MgB₄. The particle size is small and the MgB₂ is easy to decompose.