Present study conducted an empirical study on the relationship of public financial fund investment and performance of the public library information service. The findings of this research include that： 1) there is a strong effect of public financial fund invested on public libraries and the performance of these libraries at the initial stage but turn to weak gradually. 2) the public finance fund invested in public libraries affected the scale factor significantly but non-significant on the density factor partially. Based on a joint analysis procedure on the empirical findings of this research and the Hierarchical Social Cognition Theory, this study also discussed the in-depth transformation of the understanding on public libraries’ performance assessment and the reference service and hierarchical information service became the basic tendency of the public information service performed by public libraries.