After the bumps of Trump’s first 100 days in office，the development of Sino-US relations showed a more positive trend. At least the continuous building of a new model of China-US relationship is still playing a key role. In the process of pushing for the development of Sino-US relationship，the security cooperation in its initial stages needs to be carried out effectively and further fulfilled. The Asia-Pacific region is an indispensable strategic space for building a new model of China-US relationship and also where China and US have interacted for a long time，and the China-US Asia-Pacific security cooperation is key in constructing this strategic space.As active interaction between China and the US in Asia-Pacific security cooperation becomes one of the key topics in pushing for positive development of Sino-US relations，in the study of China-US Asia-Pacific security cooperation，the effect of Japan as a “third party factor” is a rare but unneglectable angle. Combined with changes in Sino-US relations since Trump came to power，as the “third party factor” in China-US interactions，Japan’s effects began to gradually show due to national strategy transformations under the second Abe administration.