A content analysis was conducted to identify the library theory of high frequency use in the past decade. We coded 15 research themes used in library theory, and classified these topics from high to low frequency use and growth through time series analysis. Five ways of the usage of theory were proposed. The content analysis of 1703 articles shows that: (1) The basic theory of library science is insufficiently explored, and new research themes such as digital humanities, big data application, academic social network and information literacy have emerged. Theoretical foundation should be constantly consolidated, and new discipline growth points should be explored. (2) The use of theory has the largest proportion of theory placement, and theory generation accounts for the smallest proportion. It is necessary to encourage theory innovation to promote the sustainable development of library science.