Abstract: Pipelines with multiple outlets are used extensively in water saving irrigation of sprinkler irrigation and microirrigation. The tapered diameter design was adopted, in which the whole multiple outlet pipeline consists of pipe segments with different diameters in such a way that the pipeline cost can be reduced on condition that the allowable pressure head difference is satisfied. The optimum design mathematic model of pipeline with multiple outlets was established for different slopes. The symbolic coding method is simple and easy to use in that the model is solved by using genetic algorithm.