This paper applies equilibrium analysis in micro-economics to analyze a stable structure in a model of human society. The structure is observed in the study of the distribution of information.It has a three-layered hierarchy and three layers are called brains, gatekeepers and end users. The three-layer structure is widely observed in a variety of research fields. For example, in computer networks, core gateways correspond to brains, stub gateways behave like gatekeepers, and local networks are just end users. The three-layer model is considered to be an essential extension of the popular "client and server" concept in computer science. This paper calculates the supply and the demand curves in micro-economics to show how the equilibrium is established. The law of diminishing utility is utilized to represent the distribution of information or knowledge. The calculations are straightforward if the dependence of the end users on the other layers is taken into account. The results can explain many properties of the three-layer model.