The invention discloses an unsaturated soil high-temperature high-pressure high-suction triaxial instrument and a sample preparation mould. The triaxial instrument comprises a rack, a pressure chamber, an axial load piston, a load sensor, a displacement sensor, an axial load and axial deformation rate control / data acquisition processing system, a water, electricity and gas control cabinet and a temperature control box with a special structure. Two models including a high-temperature, high-pressure and low-suction model and a high-temperature, high-pressure and high-suction model are researchedand developed. The operating temperature of the high-temperature, high-pressure and low-suction model ranges from normal temperature to 150 DEG C, the confining pressure of the high-temperature, high-pressure and low-suction model ranges from 0 to 10MPa, the suction of the high-temperature, high-pressure and low-suction model ranges from 0 to 1.5MPa, and the high-temperature, high-pressure and low-suction model is applicable to general unsaturated soil. The operating temperature range and the confining pressure range of the high-temperature, high-pressure and high-suction model are as same asthose of the high-temperature, high-pressure and low-suction model, the suction of the high-temperature, high-pressure and high-suction model can range from 0 to 500MPa, and the high-temperature, high-pressure and high-suction model is applicable to buffer / backfill materials. By the aid of a sample preparation device and a petal-type sample preparation mould which are matched, sample preparationand demoulding are facilitated, working efficiency is improved, disturbance for a sample in the demoulding process is decreased, and the problem of difficulty in demoulding a high-density sample prepared by a traditional method is solved.