Provided are a device and a method for synthesis of a gallium-containing garnet-structured scintillator polycrystalline material. The synthesis device includes a polycrystalline material synthesis chamber (7) made of a thermal insulation material (1); a crucible (3) arranged at the center of the bottom of the polycrystalline material synthesis chamber; an induction coil (2) annularly arranged outside the polycrystalline material synthesis chamber at a position with a height corresponding to that of the crucible; an arc heating device (4) arranged on a central axis of the induction coil in the polycrystalline material synthesis chamber, so as to heat and melt raw materials at the center of the crucible by means of the high temperature generated by arc discharge; the induction coil is connected to a RF induction power supply.