Considering research progress of complexity study and characteristic of supply chain coordination, from the relation between the complexity of a system and the amount of information which is needed to describe the state of a system, this paper proposes a quantifying model of 3-echelon supply chain coordination complexity information entropy based. The model includes two parts: supplier-manufacturer interface entropy model and manufacturer-retailer interface entropy model. Finally, through an example, gives the value of supply chain coordinating complexity and analyzes the results.