Abstract: 【Objectives】 The objective of the paper is to investigate mechanism of alternate partial root irrigation on pipe cultivated cucumber photosynthesis and water use efficiency. 【Methods】 In this experiment, using Jinyou No. 3 as experimental material, three drip irrigation patterns were set with the randomized block design: alternate partial root-zone drip irrigation (APDI), fixed partial root-zone drip irrigation (FPDI) and conventional drip irrigation (CDI). Effects of different drip irrigation methods on growth, photosynthesis and water use efficiency of cucumbers were studied under the condition of PVC pipes which separated cucumber root system to two parts.【Results】 Under APDI, the compensational growth of root system and the root activity of cucumber can be stimulated. The leaf relative water content, water potential and osmotic potential of FPDI are significantly lower than those of CDI, while the cell sap concentration is significantly higher than those of the other two treatments, which means that the FPDI treatment affects the water absorption and transport and inhibits the normal growth of cucumber to some extent. The APDI treatment significantly reduces the net photosynthetic rate and transpiration rate of cucumber leaves, but significantly improves the water use efficiency compared with the CDI treatment. The photochemical quantum yields of PSⅡ (Fv/Fm) of the APDI and CDI treatments are not significantly different, but are significantly higher than that of the FPDI treatment. The non-photochemical quenching (NPQ) of the FPDI treatment is significantly higher than those of the other two treatments, which shows that drought stress of fixed one side of the root system reduces the photochemical reaction of PSⅡand light energy use efficiency, and significantly increases the heat dissipation of the excess light energy. APDI and FPDI reduce the water consumption and seepage volume in different degrees, but FPDI severely inhibits the growth of cucumbers, while APDI not only improves the water use efficiency, but also maintains normal growth and photosynthetic metabolism of cucumber.【Conclusion】 The alternate partial root-zone drip irrigation (APDI) can be used as a water-saving irrigation pattern in protected horticulture with a broad application prospects.