The invention relates to a high-temperature and high-pressure fuel gas safety valve which comprises an upper valve body and a lower valve body. The upper valve body and the lower valve body are mutually fixed. An exhaust hole in the lower valve body is aligned to a semicircular hole in a nozzle pressure part. One hemispherical end of a valve element acts on a corrugated pipe. The other conical end of the valve element is in close fit with a gas nozzle for sealing high-temperature and high-pressure fuel gas between the lower valve body and a servo pipeline. A cooling liquid inlet is formed in an upper guiding rod on a compression spring. The upper valve body is provided with a cooling liquid outlet. A lower guiding rod of the compression spring acts on the corrugated pipe. An adjusting nut acts on the upper guiding rod of the compression spring. When pressure of the high-temperature fuel gas (over 1000 DEG C) in a system exceeds allowable pressure (about or more than 24 MPa) of the system, the surplus fuel gas in a system pipeline is exhausted so that the work safety of the system can be protected; when the pressure of the fuel gas in the system is reduced to reach the allowable pressure (about or below the 24 MPa), the pipeline is closed and sealed, and outside leakage of the fuel gas is avoided.