Abstract: In order to resolve the contradiction between the high cost of wavelength converters and their critical roles in optical networks, a new architecture of wavelength-convertible switches was put forward, and its optimal routing and wavelength assignment algorithm was proposed. Simulations were done on the NSF network to justify the advantages of the proposed architecture. Moreover, the optimal number of wavelength converters and their correct arrangement at switching nodes were obtained through the simulations. The proposed switch architecture along with the simulation tool can be effectively applied to other long-haul optical networks.