Mini-economies play a important role on the global economy.Many policy makers and researchers focus on their industry selection and expansion.By comparing on the industrial structure of typical mini-economy, it is found that the 'single industrial structure' is not the defect because it is the result of the market choice. Then using the single-period inventory model and time-series to predict the optimal scale of the Macao's gaming industry in the next three years, the result show that the demand will increase slowly in the future, the optimal scale will expand and Macao's capacity will be insufficient in 2019-2021. Based on these, this paper will propose practical and feasible policy suggestions for Macao's industry selection and expansion in Guangdong-Hong Kong-Macao Greater Bay Area.