The present invention is related to an adjustable modular drum including a first shell and plural second shells. The first shell has several lugs placed around the outer circumference, and each lug has a screw hole. Moreover, the second shells can be superimposed on the first shell. Furthermore, the drumhead on the first shell can be unloaded and then re-assembled on one of the second shells by a hoop. Then, plural tension rods are passed through the through holes around the outer circumference of the hoop and locked in the screw holes of the lugs for fixing. Accordingly, the height of the drum can be adjusted for conforming to different needs of the user without possessing multiple drums of different standards at the same time, thereby achieving the purposes of carrying convenience and reduced cost.