Under the Bumuda II Style Air Service Agreements (ASAs), passenger air traffics between 2 countries are strictly regulated by regulating bodies of both originating and destination countries. With the fast development of open sky arrangements, this approach is challenged as passenger traffics will diverse to the third country that signs open sky agreements with an originating or destination country. That is the scenario for the China-US air market. As many countries or areas like Korea, Japan, and Hong Kong, have signed open sky or more liberal agreements with US, it is attractive for many passengers to fly between China and US via those countries or areas. It means passenger losses for designated carriers of the China-US air market. This paper tries to identify the extent and main causes for passenger losses in the China-US air market. It argues that several past amendments of China- US ASA that increased flights quotas for designated carriers have effectively lowered the extent of passenger losses of the China-US air market, as those amendments significantly increased capacity of market concerned.