Abstract: Based on the analysis of hydraulic characteristics of micro-irrigation on slope with paired laterals, an optimum design method for the best submain position of paired laterals based genetic algorithms was put forward. The mathematic model was constructed, optimum arithmetic was given and computer program was also worked out. The best submain position and inlet pressure of paired laterals were ascertained. And the pressure, discharge and characteristic value of each emitter along the lateral were also figured out. Average emitter discharge of the paired lateral was equal to the design discharge of emitter, which ensured the maximal water application uniformity. Results indicate that the model and algorithms will get a solution quickly with higher precision and better reliability.