The present disclosure discloses a temperature-controllable large-size geotechnique true triaxial multi-field coupling test system and a test method. The system includes a host loading mechanism, a deformable large-size soil box, an independent three-dimensional loading unit, a refrigeration, water and salt supplementation unit, and a soil-water-ice-salt change monitoring unit. The deformable large-size soil box is arranged on the host loading mechanism. In combination with the special structural design, monitoring is carried out by dividing a large-size soil test sample into environmental soil and a core soil region to eliminate the size effect of the test. The solution can simulate a three-dimensional stress state of the soil test sample in a three-dimensional open system. In consideration of the evolution of hydrothermal salt and three-dimensional migration of temperature, water, salt, etc. between the soil and the environment, temperature-water-salt-stress-strain multi-field coupling is realized.