The operation management or readers marketing of libraries cannot be only based on the experience and intuition of the library administrators. There must be some practical evidence to provide them as a reference for decision-making. Bibliomining is the use of statistics, bibliometrics, data mining, and other techniques to analyze the data generated by library operations, to explore the information available to library managers, and to assist their decision-making. From the application of the Pareto principle in business management, it is known that analyzing vital customers can help the growth of profit of product by marketing. Also, the main profit analysis helps in effective production management. This can, of course, be used analogously to the relationship of library readers and their circulations. Whenever using library readers borrowing data to discover the 80/20 rule (or Pareto Principle) existed in library circulation, we can further discuss the issues of operation management and reader marketing of the library from three perspectives: vital readers, major collection and both. In this study, we focus on the vital readers and the major collection as research topics. Under the situation of 80/20 in library circulation, we apply data mining techniques to further explore what characteristics of vital readers, useful collections and their impacts on the library.