Being a kind of post-war institutional innovation, the Regional Trade Agreements Organization has the special evolutionary path of its origin and development. This paper has set up a theory model on ascertaining the boundary of Regional Trade Agreements Organization, which makes a conclusion that the boundary will reach the point where marginal absorb effect equals marginal exclude effect. The aggregate welfare of the Regional Trade Agreements Organization will reach the maximum in the point of boundary. There will exist four Regional Trade Agreements Organization in the world at last. China government should make scientific policies to keep the tidal wave of regional trade integration.