Abstract： In the IT industry, due to the easy proliferation and strong penetrability of IT technology, the innovation will not only spread to other upstream firms which produce imitation products, but also spread to the downstream firms. It results in the technological convergence. Therefore, from the point view of maximizing the net revenue of the whole society, the optimal patent breadth in a two ring city model consisting of upstream innovation firms and downstream convergence firms is discussed. The fact that the social welfare of technical innovation not only contains the revenue brought by upstream firms’ innovative and imitation products, but also contains the welfare brought by technological convergence of downstream firms is considered. It is shows that optimal patent breadth decreases with innovation degree, technique absorptive capacity of firms , the diversity of consumers’ preferences, and the total length of the circular city raising, but increases with the number of downstream firms and the slope of demand curve raising.