An array of aperture-coupled dielectric resonator (DR) reflectarray is used to realize a reflectarray antenna in X-band. The reflectarray composed of 23 x 23 elements and covering an area of 27.6 cm x 27.6 cm. The unit cell in reflectarray antenna consists of rectangular DRA, a slot in the ground plane, upper substrate, sub-loaded transmission line of variable length, lower substrate, and conducting ground plane. Varying the sub-loaded transmission line length can lead to 360o phase shift. The reflectarray is centered fed by linearly polarized pyramidal horn antenna. Full-wave analysis using the finite integration technique is applied. The results are validated by comparing with that calculated by transmission line method and HFSS simulator. The mutual coupling between the feeding horn and the elements of the reflectarray are considered. The 3-dB beamwidth is 8o. A peak gain of 27 dB is predicted. The reflectarray can cover from 9.5 GHz to10.75GHz, or 12.5 % bandwidth centered at 10 GHz.