Abstract:W ith regard to QoS (Quality of Service) networks, we p ropose a genetic algorithm for heuristic SP ( shortest path) routing. We use modified variable string length , and op timize GA selection, GA crossover and GA mutation. The results using C language emluator demonstrate that this algorithm can obtain a better convergence rates and reliability thanMunemoto algorithm and Inagaki algorithm, also we can find Global op timal.