The invention discloses a triaxial mechanical test device and method capable of simulating a formation condition of deep-buried artificial frozen soil. The device comprises a main body loading system,a freezing system and a sample testing system. In the main body loading system, a flange plate, a pressure bearing cylinder and a chassis form a pressure bearing shell, and the pressure bearing shellis provided with an outlet pipe and connected with an external existing hydraulic source. The freezing system is composed of a side wall freezing solution circulation channel and a bottom freezing solution circulation channel which are connected with an external existing cold source separately. In the sample testing system, an optical fiber sensor string pre-embedded in a sample is connected withan existing testing instrument and used for monitoring temperature and strain. The triaxial mechanical test device is matched with the existing servo control hydraulic source, the low-temperature cold source and the testing instrument or matched with an existing triaxial servo mechanical test machine (system), the formation condition of the deep-buried artificial frozen soil can be simulated, long-time high-pressure triaxial solidification of a soil sample is completed under the state of simulating original ground strain at first, then the soil sample is frozen under the pressure condition toform a frozen soil sample, and a triaxial mechanical test for the frozen soil sample is conducted.