Abstract: A simple, direct, and easily adaptable analytical approach was developed for determining the appropriate diameter of the drip laterals laid on uniformly sloping grounds. The emitter flow variation was used as the index of water application uniformity. A diameter design parameter was developed by reformulating the analytical expressions of emitter flow variation of the single inlet lateral and paired laterals. The relationship between parameter and pressure loss ratio were expressed by the graphs and formulas. For the specific value of velocity exponent, the condition for designing the diameter of a single inlet lateral was the calculation parameter lying between -1 and ≤2.801, between -1 and ≤2.859 and between-1 and ≤4, respectively; meanwhile, the condition for designing the diameter of the paired laterals was the calculation parameter lying between 0 and ≤3.143, between 0 and ≤3.183 and between 0 and ≤4, respectively. On the other hand, for the required emitter flow variation and emitter design discharge, there would be one or two solutions of diameter for a single inlet lateral, and one, two or numerous solutions for the paired laterals. Based on the ranges of the parameter, the design equations for the diameter of the single inlet lateral and paired laterals were derived with the pressure loss ratio as the design variable. The analytical expressions of inlet working pressure head of drip laterals were also simplified based on the energy gradient line method. When the emitter design flow, emitter flow variation criterion, and lateral length were provided, the diameter and inlet working pressure head of the drip laterals could be easily calculated without performing complex computer operations or tedious computations. In case 1, the differences in the designed parameters of a single inlet lateral from the proposed approach and variable discharge method are less than 4% for most ground slopes. In case 2, the maximum deviation in the design parameters of the paired laterals from the proposed approach and previous two methods was ≤4%. These 2 cases indicated that the proposed approach could produce accurate results as those of the previous methods for practical purposes. By using the developed analytical expressions and regression relationships, the proposed approach provided a more simplified and adaptable design procedure than the traditional methods. This research could provide valuable information for improving the hydraulic design of drip irrigation system.