Fine roots (diameter, <2 mm) play an important role in global biogeochemical cycle. They are the core linkage for material and energy exchange between plants and soil. Elucidation of the distribution of fine-root standing crop (SC) could improve our understanding of fine root growth pattern and thus guide vegetation construction. In this study, we used the minirhizotron technique to determine the fine-root SC of young (5 years) and mature (30 years) Caragana korshinskii plantations in situ in the northwest Shanxi Province. We compared the temporal and spatial patterns of fine-root SC between the young and mature plantations on the basis of observational data collected during 2008-2011. Responses of fine-root SC to environmental factors (precipitation, soil temperature, and soil moisture) were also analyzed. The following results were obtained: (1) In the 0-100cm soil profile, maximum fine-root SC in both the plantations occurred below the depth of 50 cm. However, most active depths for fine roots in mature and young plantations were not consistent. Fine-root SC in mature plantations were the highest in 50-60cm soil depth, whereas they were the highest in 90-100cm soil depth from March 2008 to September 2010 and in 80-90cm depth from October 2010 to October 2011 for the younger plantations. The vertical pattern was a single peak curve for the mature plantations in the 0-100cm soil profile, but not for the younger plantations. This pattern was mainly affected by soil moisture. Fine roots in young plantations were more sensitive to soil moisture than those of mature plantations. (2) During 2008-2011, relatively high fine-root SC was observed in March and April. Fine-root SC in the 0-30cm soil layer exhibited similar seasonal pattern as precipitation. However, in the 30-100cm soil layer, seasonal pattern of fine-root SC was similar to temperature variations. In the 30-100cm soil layer, the occurrence of maximum fine-root SC in young plantations was earlier than that in mature plantations. In September and October, fine-root SC in young plantations decreased faster than that in mature plantations. From June 2009 to the end of the observation, fine-root SC of mature plantations was higher than that in young plantations. The difference among mean annual fine-root SC was mainly affected by interannual precipitation variation, whereas seasonal dynamics within the calendar year were mainly driven by temperature. (3) In the 80-100cm soil layer, the soil moisture was higher in young plantations than in mature ones. The soil temperature in young plantations increased faster than that in mature ones at the beginning and decreased faster in young plantations at the end of the growing season. In summary, fine roots of C. korshinskii were mainly distributed below 50cm soil depth. Fine roots of young plantations were distributed at a deeper depth than those of the mature ones. This vertical pattern was mainly affected by soil moisture. The occurrence of maximum SC in young plantations was earlier than that in mature plantations. Such seasonal changes of fine-root SC were controlled by soil temperature. Compared to the fine roots in mature plantations, those in young plantations were more easily affected by environmental factors such as precipitation, soil moisture, and soil temperature.