中文摘要：

节水灌溉工程设计是推广节水灌溉技术的关键环节，毛管的水头损失计算是滴灌工程设计与运行的重要技术参数之一。目前的设计手册无直接推求毛管水头损失的计算公式，传统方法需要计算多口系数、按经验给定局部损失扩大系数等，计算过程复杂，且对经验性要求较高。通过对毛管整个管段进行微分，并采用数学变换，逐步优化拟合原理，得到均匀坡毛管水头损失的直接计算公式，该式不需给定孔口扩大系数、推求多口系数，而且适用范围广泛，精度评价满足工程需求，且物理概念清晰明确。实例工程应用及误差分析表明：在实例工程中误差仅为0．57％，在工程应用范围内误差集中分布在1％内，为滴灌工程设计手册的编制和设计人员提供有益的参考。

英文摘要：

The design of water-saving irrigation is the key to promoting water-saving irrigation, The head loss calculation of capillary is one of the important technical parameters while designing and operating drip irrigation system. There are no direct formula for cal- culating head loss of capillary in the current design manual calculating, traditional methods must calculate muti-port coefficient, give expansion coefficient of partial loss by experience, etc, computation process is complex. In this paper, through differentiating on the whole pipe of capillary, using the principle of mathematical transformation, optimization and fitting, and in the end get the direct calcu- lation formula direct calculation formula,This formula need not give orifice expansion coefficient and calculate muti-port coefficient, having broad range and assessment of accuracy be satisfy for design requirement, having clear and simple of this formula. Results of the example calculation and error analysis show that the relative error of tradition methods is 0.57%. The relative error of this for- mula applied for engineering contagious distributed within 1%,which serves as a reference to manual compilation of engineering de- sign and irrigation design.