Abstract: Drip irrigation with harvested water in pits is becoming an important solution to water resource shortage in the arid and semi-arid areas of West and North west China. The water harvesting pits are featured with their characteristics, such as small in water storing capacity, sparsely distributed, difficult in pipeline layout and complicated in system management. Based on irrigating crops at the key growth stages, main pipe used for water supply and laterals were used to deliver water into individually distributed field plots, in aim of reducing investment and for the convenience of irrigation management. An optimization design method was advanced to design the optimal water supply lines, for the purpose of supplying water from various water resources of pits to numerous crop plots with a unified pipe system. The method was compared with both the traditional method and graph theory method to validate its feasibility. The new method is applicable to the design of water supply pipe lines in drip irrigation systems under distributed crop fields and water resources from water harvesting pits.