In a wavelength routing optical network (WRON), the optimal allocation of wavelength converters (WCs) is very important to minimize the number of WCs, enhance the fiber utilization, reduce the blocking probability, etc.. In this paper, a novel simplified network model with shared WCs has been proposed. An effective algorithm for optimal allocation of shared WCs has been presented by using a revised Dijkstra algorithm and genetic algorithm (GA). The effectiveness of the revised algorithm was verified through the simulation on Nature and Science Foundation (NSF) net of USA. This revised algorithm can achieve blocking probability 36% less than the algorithm in previous work, and the calculating time of the minimum blocking probability can be reduced dramatically.