The utility model discloses a preparation device for a remolded soil tri-axial compression test sample. The preparation device comprises an upper pressing plate, a base, a transverse plate, air exhaust holes and air exhaust grooves, wherein a sample preparation chamber is formed by the upper pressing plate, the base and the transverse plate; the air exhaust grooves are formed in the upper pressing plate; the air exhaust holes are formed between the air exhaust grooves. The problems that a remolded sample is unevenly manufactured and dry density and water content are difficult to control are solved by virtue of a transverse compaction sample; the dry density of the tri-axial compression test sample can be effectively controlled, the sample is smoothly manufactured, requirements for related specification sample manufacturing accuracy are met, the device is convenient to operate, and the sample is easy to disassemble; by virtue of the air exhaust grooves and the air exhaust holes, the problem of air exhaust in the sample preparation process of fine-grained soil is solved, friction caused by downward movement of the upper pressing plate is reduced, and external force needed by the press-down process is decreased.