The effects of long-term application of organic fertilizer on the yield and water use efficiency of rain-fed potato and the stability of soil aggregate structure in the semi-arid region of Northwest China were studied based on the long-term positioning experiment of National Soil Anding District Observation and Experiment Station of Gansu Academy of Agricultural Sciences.The results showed that fertilization significantly affected potato yield and water use efficiency through 8 years of positioning fertilizer experiment.Organic fertilizer combined with chemical fertilizer(NPKM)treatment had the best effect，followed by organic fertilizer alone(OM)treatment .Compared with single-application fertilizer(NPK)treatment，long-term application of organic fertilizer(NPKM and OM)treatment increased potato yield by 24.4% and 17.5%，and water use efficiency by 32.2% and 22.0%，respectively.The soil water stability aggregate composition in the loess hilly and gully region increased in step with the decrease of particle size，and the micro-aggregate <0.25 mm occupied the dominant level，with the proportion of 41.9%-75.8%.Compared with CK，the agglomeration degree of 0-20 cm soil in the topsoil under different fertilization treatments increased significantly，and NPKM treatment had the best effect.Compared with NPK treatment，the water stable aggregates of soil with diameter >2，1-2，0.5-1 and 0.25-0.5 mm were increased by 169.4%，49.5%，206.4% and 28.8%，respectively，while the water stable aggregates of soil with diameter <0.25 mm was decreased by 31%.Compared with NPK treatment，NPKM and OM treatment significantly increased the content of > 0.25 mm aggregates(R0.25)，mean weight diameter(MWD)and geometric mean diameter(GMD).NPK treatment significantly increased the content of 0.25-0.5 mm water-stable aggregates compared with CK.In summary，under the condition of loessial soil in the loess hilly and gully region of Northwest China，long-term application of organic fertilizer significantly affected potato yield and water use efficiency in extremely dry years，and the effect of NPKM treatment was the most obvious.Compared with NPK treatment，it significantly increased the particle size content of water-stable macroaggregates(0.25-2 mm)and the MWD and GMD of aggregates，promoted the formation of soil aggregates，and enhanced the stability of aggregates.