The invention discloses a vertical polysaccharide high-polymer mechanical activation constant-temperature solid-phase reactor. The reactor comprises an outer barrel, and a grinding inner barrel is sleeved with the outer barrel in a sealed mode. A stirring device and a plurality of grinding balls are arranged in the grinding inner barrel, and a stirring shaft of the stirring device penetrates through a cover plate and is connected with a driving device. A plurality of annular channels are formed in the outer wall of the grinding inner barrel from top to bottom. A jacket is formed by the channels and the inner wall of the outer barrel, and a working medium inlet and a working medium outlet which extend to the outside and are communicated with the channels are formed in the jacket, so that heat exchange working media are introduced to cool or heat materials in the grinding inner barrel. A plurality of cylinders are arranged on the inner wall of the grinding inner barrel, temperature measuring holes are formed in the cylinders, and temperature monitoring devices are mounted in the temperature measuring holes. Temperature signals collected by the temperature monitoring devices are fed back to a heat exchange device for conducting temperature control and circulation on the heat exchange working media and a flow control device so as to control the temperature and flow of the heat exchange working media. By the adoption of the reactor, the materials can be evenly mixed, the reaction temperature is stable, monitoring is easy, and the quality of obtained products is high.