Abstract: The micro-irrigation technique of gravitational flexible hose is a very practical water-saving irrigation, which is widely popularized in Xinjiang Region and has extensive application prospects in the present economic and technological condition. Based on indoor experiments, the hydraulic characteristic of the gravitational flexible hose was analyzed by combining hydraulic theory and mathematics knowledge. The method for determining the optimal laying length of gravitational flexible hose was proposed. And the suitable laying length that could satisfy the degree of consistency was provided. The theory results are consistent with the successful project experiences. Combining the project examples, this paper presents the designing steps, which provides references for planning and designing the gravitational flexible hose.