Abstract: The objective of this study was to explore the effect of fertilizer application on the stem length and diameter of alfalfa planting in Horqin Sandy Land. To reveal the variation law of stem diameter and length of alfalfa, demonstrate the growth status of alfalfa and provide theoretical basis for fertilizer application in alfalfa planting, a field trial was conducted by setting different fertilizer amount and fertilization frequency. The results showed that the increased amount of fertilizer promoted the elongation growth of stem of the first-cut alfalfa, while its growth was inhibited by excessive fertilizer use. The increased fertilization frequency had no obvious effect on stem length of the second-cut alfalfa when the fertilizer amount ranged from 50 to 70 kg/667 m2. The average value of stem length and diameter of the three cuts of alfalfa was the second-cut 〉 the first-cut 〉 the third-cut and the first-cut 〉 the second-cut 〉 the third-cut, respectively, and the average value of stem length to diameter ratio of the three cuts of alfalfa was 186.68, 291.70 and 298.80, respectively. The fluctuation range of the stem diameter of the three cuts of alfalfa was 2.92-3.99 mm, 2.47-3.13 mm, 1.52-2.28 mm, respectively. There was a significant linear correlation between stem diameter and length.