At present, unconfined compression tests for solid particle systems are all executed at room temperature, while in actual engineering, many solid particle systems are in high-temperature environments,and a device for measuring compressive strength of the solid particle systems at the high temperature is needed. Therefore, the invention provides a high-temperature unconfined pressure instrument. The high-temperature unconfined pressure instrument comprises a force measuring ring, a scale, a connecting rod, an upper pressing plate, a lower pressing plate, a screw, a pressing frame, a hand wheel, a support frame, a high-temperature electric heating furnace, heating elements, a temperature measuring element, a temperature control device, a furnace wall, a furnace door and a test sample, can perform unconfined compressive strength tests on the solid particle systems at the high temperature and can accurately measure the unconfined compressive strength of the solid particle systems at the high temperature.