Abstract: Arrangement mode that both sides of the branch pipe of micro-irrigation system with paired capillaries has advantages of investment-saving, energy-saving and high quality of irrigation. Based on hydraulics with limited holes in capillary, methods of determining locations of branch pipe on slope with paired capillaries was discussed: four cases in calculations; the corresponding analytical formula; trial calculation of formula on reasonable holes; length of entrance region; improved formula of enlargement coefficient of total loss in entrance region of capillaries. The basic principle of determining locations of branch pipe or length of capillaries is the equality of entrance water head in paired capillaries on the basis of average discharge of emitters in paired capillaries equaling design discharge. Two steps should be followed: 1) choosing the proper algorithm and determining holes by trial calculation; 2) calculating water head of the first hole in upper reaches of paired capillaries and the corresponding length of entrance region. If two water head of the first hole are approximately equal, the corresponding entrance region could be considered as the same length. Numerical examples shows methods proposed in this paper can be applied in micro-irrigation system design and have references in main pipe arrangement of spray irrigation.