A practically study had been effectuated in the farm of faculty of agriculture – sana'a university. It aim to improve the drip irrigation system's emission uniformity of closed designs (C1D, C2PD, C2OD), for deferent lateral sizes (14, 18, 22mm of ID), using various in emitter flow types (Turbulent, Laminar, PC), under three operating pressure (0.8, 1.0, 1.2 bar). Number of laterals was 9 of 90m length and 1m of lateral spacing, where the flow rate for all emitters was constant (8.0l/h) and emitters spacing along the same lateral line was 0.5m. The results shows that: The closed design system (C2OD) record the highest value of emission uniformity (average of 93.223%), comparing with closed design systems (C2PD, C1D) of 91.9375 and 88.559% average emission uniformity respectively. The closed design system (C2PD) represented the best pressure distribution along the lateral length comparing with C2PD and C1D closed system designs. The closed design system C1D record the highest friction head losses of 1.277m in average, comparing with closed design systems C2OD and C2PD (0.37 and 0.373m respectively). The closed design system C2OD results the highest average emitter discharge value of 7.77L/h, comparing with closed system designs C2PD and C1D that recorded average emitter discharge values of 7.56 and 7.33 L/h respectively. The closed design system C2OD increases the value minimum emitter discharge to 7.58L/h, where the closed design systems C2PD and C1D recorded 7.44 and 6.88L/h respectively. The lateral size of 22mm ID record the lowest friction head losses of 0.178m (0.507 and 1.48m for C2PD and C1D respectively) that resulting in highest emission uniformity of 91.717% comparing with 90.2995 and 89.9065 for C2PD and C1D design systems respectively. The operating pressure of 1 bar results the highest emission uniformity of 91.3365 comparing with 1.2 and 0.8bar of 91.0705 and 89.9005 emission uniformity percentage respectively. The pressure compensating emitter record the highest value of emission uniformity (92.9162%) comparing with turbulent and laminar flow emitters of 91.6215% and 88.342% respectively.