The invention relates to a fixed bed reactor which is provided with a quartz reaction tube at the central of a right shell of a flange sealing face; one end of the quartz reaction tube to the flange sealing face is communicated with the inner chamber of the reactor and the other end extends outside the shell; the quartz reaction tube is externally sheathed with an electric heater unit; the centerof a left shell of the flange sealing face is provided with an air through pipe; the right end of the air through pipe is butted with the left end of the quartz reaction tube and is communicated withthe inner chamber of the reactor and the other end extends outside the shell; the shell of the fixed bed reactor is filled with high temperature material so that the temperature of the wall of a reaction high temperature conductive device is reduced below 50 DEG C; the quartz reaction tube is butted with the air through pipe at the flange sealing face so that the inside and outside pressure of the quartz tube is equal during high temperature reaction; the quartz tube is sheathed with the electric heater unit for directly heating reaction gas, thus greatly increasing heat transfer efficiency and saving power source. The fixed bed reactor is suitable for high temperature and high pressure reaction conditions of methane carbon dioxide reforming reaction, and has simple structure and convenient operation.