Abstract: A cover assembly for a portable hard disk comprises an assembling unit having a frame hole at a front side thereof; the assembling unit having an opening; the opening causing the assembling unit being divided into an upper portion and a lower portion; two ribs serving to divide the frame hole and the opening; a chain being movably installed to the opening; a hard disk combined to the circuit unit; the circuit unit having holes corresponding to a bottom of the hard disk; an upper cover combining to an upper side of the upper portion of the assembling unit; a base combining to a lower side of the lower portion of the assembling unit and being almost identical to the cover; the upper cover and the base being formed with a space for receiving a data storage unit.