According to David Legato's comparative advantage theory, all developing countries with advantageous resources have not reached sustainable development and economic growth through exporting resources, implying that the static comparative advantage theory has deficiencies. This paper, based on a revised comparative advantage theory, establishes a dynamic comparative advantage model, analyzes the trading welfare under free trading conditions, draws a conclusion that the free trading conditions will definitely decrease the welfare, and presents some suggestions how to make policies for China's resource industry via a dynamic comparative advantage theory.