Changes in soil properties during long-term planting require thorough study. The objectives of this study were to determine the influence of planting Caragana microphylla on grassland on soil carbon, nitrogen, and phosphorus to a depth of 20 cm along a 34-year chronosequence encompassing 10 plantation-age groups in northwest, China. We found soil organic carbon increased by -21.84%, 0%, and 39.09% in planting years 5, 21, and 34, respectively. Total nitrogen and total phosphorus began to change in the plantation years 9 and 7, and increased by 70.59% and -28.26% in year 34. Both available nitrogen and available phosphorus increased across the chronosequence. The results indicate that the processes of changes in soil carbon, nitrogen, and phosphorus are different in a long-term chronosequence, and that Caragana microphylla has potential to improve soil properties after it is planted on grassland.