An improved growth model was established by adding a stressing factor to classical Logistic model.The growth data of Caragana microphylla shrubland was collected in semi-arid loess hilly region,Guyuan City of Ningxia Hui Autonomous Region,to which the new model was fitted.The result showed that the improved model is highly sensitive to the planting density.The optimal density of caragana in the study area should be limited in the range from 51 to 71 clusters per one hundred square meters.