If all material units in the economic entities (including inorganic substances and organisms) can fully realize value circulation, the entities will be able to produce the largest total value. Total value refers to the “net value” by subtracting “negative value” from “positive value”. The “positive value” is the direct value of products provided by the economic entities, and the “negative value” refers to the value loss caused by the negative influence of economic entities on resource environment and social economy. This paper makes exposition of circular economy from three aspects: circulation of material units in the production process within economic entities is the core of circular economy; circular economy aims at bringing material units out the economic entities by being affiliated to products; branding material units with value for recycling in economic entities is the guarantee of circular economy.