Abstract: This paper demonstrates that cartographic symbol system belongs to Boolean algebraic one according to Boolean algebraic definitions and sufficient conditions. The graded principle of cartographic symbol system and its constituted methods are expressed by defining the relation of equal value in cartographic symbol system. The theoretical value and practical meaning of structure map contents by multi-level algebraic operation in computer-aided cartographic are researched. Because Boolean algebra is a system suitable for logic operation of computer, it provides wide prospects for the exploitation and application of the software of computer-aided cartography.