A tray structure includes a plurality of trays stacking together from top to bottom and expanding in an alternating manner to construct a spiral plant tower. Each of the trays includes a bottom plate, a peripheral wall and a cultivating space. Each of the trays includes an inner tube provided with a protruding locking member, and an outer tube provided with a plurality of recessed locking members. The recessed locking members of the outer tube of an upper one of the trays are locked onto the protruding locking member of the inner tube of a lower one of the trays. Each of the trays includes a connecting tube located in and connected with the inner tube by a plurality of separating ribs. The connecting tubes of the trays are juxtaposed to each other when the trays are combined together.
