The invention discloses a fuel oil and gas boiler with an external high-temperature superheater which comprises a boiler body, wherein a lower-temperature superheater is arranged in convection pipe bundles in the boiler body, a lower-temperature super-heated steam outlet matched with the lower-temperature superheater is arranged on the boiler body and is communicated with a high-temperature superheater assembly arranged outside the boiler body through a pipeline, the high-temperature superheater assembly comprises a combustor, an ignition and pre-combustion chamber and an air-mixing chamber, a cold-blast air inlet is arranged on the air-mixing chamber, the high-temperature superheater is arranged in the air-mixing chamber and is provided with a high-temperature super-heated steam inlet and a high-temperature super-heated steam outlet, and the high-temperature super-heated steam inlet and the high-temperature super-heated steam outlet are communicated with a main steam outlet through pipelines; the high-temperature superheater of the fuel oil and gas boiler is arranged outside the boiler body, the operating conditions of the high-temperature superheater are improved, the safety and reliability of the high-temperature superheater are higher, the service life is long; and at the same time, the high-temperature superheater can operate or can be stopped as required, so as to meet the need of steam use by users at different time.