The design of micro-irrigation laterals affects the project cost and irrigated quality. This paper put forward a kind of optimization method based on genetic algorithms for bidirectional flow laterals diameter on sloping field. This method could get the optimal diameter and control criterion of irrigated quality such as average flow and uniformity. Meanwhile, the running control parameter such as the optimum crotched position and intake pressure of laterals could be determined. The example's result shows, model and algorithms solve time as 9 s, computing accuracy to attain 0.001%, having good and in general use and function.