In this paper，through the study of the structure of Macao's gambling，we build a System Dynamics model of Macao's gambling revenue.Through the calculation，only if gross income of gambling is more than 21 billion every month，then gambling enterprise can get a normal profit，and the government can meet the budget，have enough resources to implement expansionary fiscal policy，and also can maintain the current welfare level of the residents.In order to guarantee the numerical value，by building a System Dynamics model，we suggest to open the number of free line is up to about 2 million.At the same time，taking the bearing capacity of Macao society into consideration，we suggest that we should increase 1 million people every year in 2 years；that is，we should increase 250000 people quarterly.