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A 5 year field experiment was conducted to investigate the influence of different yearly climatic features and row spacing on seed yield and seed yield components during the 2008-2012 growing seasons in semi-arid soils in northwest China. Rows pacing treatments were 30, 60, 90, and 120 cm. Seed yield and some seed yield components were determined for all treatments. The year affected seed yield components markedly, but row spacing except for the quantity of seeds per pod. The interaction of year and row spacing have a significant impact on racemes per square meter and seed yield (P < 0.05). The highest seed yield was gained in the fifth year (409.83 kg ha(-1)) with 60 cm row spacing (456.30kg ha(-1)). These results indicated that alfalfa should be planted with 60cm row spacing, which was most productive for improving the alfalfa seed yield in semi-arid lands.