The aim of this research was to investigate the performance of three bubbler tube diameters at three initial operating pressure of 15, 30, 45 kPa to determine optimum operating conditions that achieve high discharge uniformity Cu. The coefficient of uniformity (Cu) was evaluated in two cases. First, when bubbler outlets heights were at the same level at 0.0, 0.2, 0.4, 0.6, 0.8 and 1.0 m. The results show that the highest values of the coefficient of uniformity were obtained from initial operating pressure of 30 kPa and internal bubbler tube diameters of 5.2 mm where values were almost constant with average 99.3%. Second, when bubbler outlets were parallel to the hydraulic gradient line with three effective heads for each initial operating pressure. The results show that all bubbler tubes along the lateral line give the same discharge for ID 3.8 and 5.2 mm, but the discharge different for 13.6 mm bubbler tube diameter. The recommended bubbler diameter was 5.2 mm at 30 kPa initial operating pressure to achieve high discharge uniformity; In addition, it achieves higher lateral line length than 3.8 mm bubbler diameter to minimize initial irrigation system cost.  Also, bubbler diameters 13.6 mm are not recommended for low-head bubbler systems due to poor water distribution uniformity.