Researchers of Marxist theory generally believe that Marx's concept of economic basis refers to the sum of social production relations at a certain stage, while the concept of superstructure has two meanings: system and concept. In fact, this is a misunderstanding of the concepts of economic foundation and superstructure. In understanding Marx's concept of economic basis, researchers confused the concept of economic basis and social economic structure; while thinking about Marx's concept of superstructure, they incorporate the system into the superstructure incorrectly. This paper holds that Marx's concept of economic foundation has two meanings: synchronicity (productive forces and productive relations determined by productive forces) and diachronism (contradictory movement of productive forces and productive relations). The concept of superstructure means superstructure of concepts.