In the July of 2020, IFLA issued a report Library's ROI----Review of Cases in the Last Ten Years in which outlines were given about studies and evaluations of the ROI of public libraries, university libraries and professional libraries all over the world in the last years, and different methods were introduced concerning the assessment of library work and ROI. Through an interpretation of the report, the author believes that libraries in our country should change our ideas about library, pay more attention to the study of assessment of economic value, and the assessment should be regarded as library's normal autonomous work. The industry association should play the leading role in advocating and organizing the assessment, and in order to make the assessment more credible, professional evaluating agencies can be invited to take part in the job. The assessing methods should be improved gradually to fit to the actual situation of our country and the specific library.