In this paper, after presenting the functions of the wavelength converter in all-optical networks, we educe and analyze the blocking probabilities of the network. Based on the above, we propose an algorithm for allocating wavelength converters in all-optical networks and use the computer simulations to evaluate the performance of the proposed allocation algorithm. The simulation results show that the performance of our algorithm is close to that of the optimal ones in terms of blocking probabilities. However, the time complexity of our algorithm is only O(3H+ w2/2).