Abstract: This paper studies the legislative decision-making service of the Library of Congress from the perspective of think-tank construction, to provide reference for the other libraries. With the methods of literature survey, network survey and case analysis, the legislative decision-making service of four departments of the Library of Congress is investigated, while its think-tank service strategy is analyzed from four aspects of the organization, resources, achievements, application and impact. The related service promotion strategy for the libraries of China is put forward as a result. The legislative decision-making think-tank service promotion strategies of the library include strengthening the resources construction and research service of the support department in the organizational structure aspect, obtaining the support from the professionals both inside and outside the library in various forms in terms of resource allocation, giving play to the think-tank role of the scholars, establishing the communication mechanism in term of the service form, and focusing on the support of the national and local key developing areas regarding service content.