Abstract: With the rapid development of computer technology, big data has a great impact on the reader service of library. This paper expounded the concept, characteristics and application of big data, and analyzed the current situation of readers' work in university library in the era of big data by using the function of measurement and visualization of CNKI, and studied the great challenges faced by library's reader service, and pointed out that librarians should be creative, and reform the shortcomings of library's reader service, effectively grasp the multi-level needs of readers and provide readers with a wide range of service.