The invention discloses a method and a device for determining the high-temperature phase composition of fireproof materials. The method and the device are used for accurately determining the phase composition of the fireproof materials at different temperatures and also can be used for observing certain fireproof materials of which microstructures can be reserved through quenching at high temperature. According to the method and the device, a computer and an electric stove with the maximum heating temperature of 1,800 DEG C are adopted, a corundum slide plate with a slideway is placed at the bottom of a stove body, a circular hole is formed in an end part of the corundum slide plate and is communicated with a cooling device, and a pushing mechanism is arranged outside a stove chamber; samples are fireproof products or powdered materials; and the samples are placed on a corundum gasket, are subjected to heating, insulation and cooling, are subjected to mineral composition analysis by using an X-ray diffractometer and are subjected to microstructure analysis by using a scanning electronic microscope and an optical microscope. The device disclosed by the invention is designed based on ordinary high-temperature test stoves and is simple in structure, low in cost, convenient in operation and good in determined data reproducibility.