Abstract: The effects of pipe length, emitter spacing and operating pressure of drip irrigation laterals on their total head loss were studied in this work using laboratory tests. The results showed that the total head loss was increased with inlet pressure or pipe length, but decreased with emitter spacing. Of these three factors, the variation in head losses caused by inlet pressure took the mildest trend. In the complicated calculation procedure of a drip lateral, six physical parameters were considered: mean inlet velocity υ0, drip lateral diameter D, pipe length L, emitter spacing s, kinematic viscosity of water ν, and gravitational acceleration g. We have developed a multiple regression model using four dimensionless variables of υ0D/ν，υ02/gD，LD/s2 and ε (contraction ratio of the emitter installation section) for prediction of head loss. By this model, we derived a formula for calculation of the energy loss and formulated a method to determine the pressure at any location along the drip lateral through analysis of the corresponding energy gradient. The predicted values agree well with the experimental measurements. Our results would help hydraulic design and evaluation of drip irrigation systems.