The study area was located in the Huanghuaidian sub-basin of Aohanqi, Inner Mongolia, and 5 clusters of samples were selected in the ten-year-old Caragana korshinskii plantation, on the slope and the slope.The roots were collected by a quarter circle method, and the standard plexus root system was divided into fine root, middle root and bone root.The length and the content of free amino acid were measured.By comparing the differences in the length of each root of the different soil moisture content, the content of free amino acids in the roots of the two species was compared and analyzed.The trend of free amino acid and free proline in different soil water content and the trend of free amino acid average content and root length were obtained.The results show: (1) The length and free proline content of the major organs were negatively correlated with soil water content.(2) There was a positive correlation between the free proline content and the root system.(3) The correlation coefficients of free amino acid content between the two groups were between 0.980 and 0.997, and the correlation was significant.(4) There was a positive correlation between the average content of free proline and the specific surface area of fine roots and R2=0.9371.It is proved that free proline plays an important role in plant resistance to drought stress and provides scientific basis for vegetation restoration of Caragana korshinskii and the interlaced zone of agriculture and grazing in Inner Mongolia.