FTA construction has been the focus of Hong Kong's economic issues under the background of “The Belt and Road”.Hong Kong，as a small economy with a weak economic foundation and a single industrial structure，does not have the ability to oppose free trade in the wave of globalization.Therefore，opening is the only outlet.Based on the GTAP9 simulation analysis of economic effects before and after Hong Kong's joining the FTA，the results show that：（1）Hong Kong's joining the FTA may not bring benefits，but it is bound to be harmful than good if not.（2）Hong Kong's joining the FTA alone lacks sufficient attraction；（3）The scale of the FTA economy is highly relevant to the impact on Hong Kong.In the end，this study puts forward the FTA construction strategy of “multi-echelon echelon” integration into the Mainland under the background of “The Belt and Road”，and as well as taking a ride from nation to promote the FTA construction，and focus on seeking large-scale multilateral FTA policy recommendations.