MgB
2 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 MgB
2 phase has synthesized without other impurities such as MgB
4. The particle size is small and the MgB
2 is easy to decompose.