Abstract: A volume-changeable van compartment including an outer wall and an inner wall wherein four hydraulic cylinders are disposed on the inner wall to lift/lower the outer wall, and an equilibration mechanism for keeping the hydraulic cylinders operating at same speed, and a locking mechanism for locking up the outer wall at a certain height, a plurality of vertical male rails being evenly disposed on the outer wall and a plurality of corresponding female rails being disposed on the inner wall whereby the hydraulic cylinders can operate to lift/lower the outer wall for enlarging the volume of the van compartment, on two sides of each of the female rails being formed a groove whereby a wall board can be disposed between two adjacent female rails to form a portion of the inner wall.