In this paper, a new relation called virtual-real relation in research of deductive database system has been proposed, virtual-real relation can integrate some advantage of real relation and virtual relation, overcome some disadvantage of them, it has a special character in DDBS. After introducing virtual-real relation to DDBS the authors can extend the function of DDBS. Now a virtual-real relation has been realized in DDBS -dUNIFY on SUN-3 workstation and is being applied to CAD and graphic fields.