This paper reviews and evaluates the 2008-2009 Inter-Sessional year of the ARF. It points out that the ARF as the only multilateral security cooperation institution on the government’s level in the Asia-Pacific region is now undergoing transformation from only discuss principles to discuss both principles and concrete matters. The ARF also provides an important platform for the US to deeply involve in multilateral security cooperation process in the Asia-Pacific，and expands it’s multilateral diplomacy;but the capability of the ARF still is limited when it handle with important and sensitive security agenda. ASEAN’s role and its activities in the ARF，regime building of the ARF，China’s participation and contribution will be the main factors affecting the future of the ARF.