Fine root was a major organ of trees in absorbing water and nutrients. The growth and development of trees were influenced by the spatial distribution of fine roots in soil. It is important and significant to know the spatial distribution pattern of fine roots for evaluating the competition among tree species and understanding the utilization status of the available resources belowground. In this study, we investigated the spatial distribution and seasonal dynamics of fine roots in a 30-year old Caragana korshinskii with the minirhizotron technique in the Northwest Shanxi, which belongs to the Loess Plateau region of China, during the growing season (from April to November)in 2007. The minirhizotron tubes were installed at three horizontal distances (0 cm, 50 cm and 100 cm) from the plant stems within the 100 cm soil depth. The results showed that (1) the average root length density (RLD) of Caragana korshinskii was 1.3423 mm/cm² in the growth season. RLD exhibited the trends of first increase then decrease in both horizontal and vertical directions. In horizontal direction, the biggest value of RLD (1.5369 mm/cm²) appeared at 50 cm from the plant stems, but the smallest one (1.1044 mm/cm²) emerged at 100 cm from the plant stems, and there was no significant differences in RLD among the three horizontal sites (P> 0.05). In vertical direction, the value of RLD ranked as: 40-60 cm>60-80 cm>20-40 cm>0-20 cm>80-100 cm, and there was a significant difference in RLD among the five soil layers (P<0.05); (2) the monthly average RLD within the 100 cm soil depth changed from 0.4405 to 2.1040 mm/cm² in the growth season. The biggest RLD was found in September, and the smallest one occurred in April. There also existed the trend of first increase then decrease for the seasonal change of RLD in either each soil layer or each horizontal site, and their maximum values of RLD appeared in the period from August to October, and the minimum values mostly presented in April or May. The season changes of RLD among different soil layershad significant differences (P<0.01), however, the season changes of RLD among different horizontal distances manifested insignificance (P> 0.05). Results from the analysis of simple and multiple correlations indicated that there existed different correlations between RLD and each factor or multiple factors (soil temperature, moisture and nitrogen availability) at different soil layers and different horizontal distances. RLD might be mainly influenced by soil moisture in 0 20cm soil layer, and impacted by soil temperature in 80 100cm soil layer. However, in other soil layers, RLD could be synthetically affected by soil temperature, moisture and soil nitrogen availability. It suggested that the change characteristics of spatial distribution and seasonal dynamics of fine roots in this C. korshinskii plantation may be resulted from spatial and seasonal heterogeneities of the soil properties. However, more observations should be conducted to test the effects of fungi and herbivorous insects on the fine roots because many researches showed that fungi and herbivorous insects might also influence the growth of fine roots.