Caryopteris mongolica, a rare and endangered small shrub, is mainly found in arid grasslands in northern China. Its distribution areas have rapidly contracted in recent years. In this study, an attempt was made to investigate the causes of the low survival rate of seedlings under local field conditions. The study combined a field survey of seedling survival with laboratory assessments of seed germination and seedling growth under different environmental conditions to establish the difficulties for C. mongolica seedling establishment. We selected a C. mongolica community in arid grasslands. The survival capacity of seedlings, seed germination, and seedling establishment under different temperatures, water cycles, and water quantities were determined. Climate and soil conditions were also studied. The following results were obtained. (1) Under field conditions, a large number of seeds germinated during the period from May to July, but few seedlings survived due to a high seedling mortality. The natural regeneration rate for the plant seedlings was 0.11 plant/m², because of the very high mortality rate of seedlings. (2) Seeds of C. mongolica had no dormancy after ripening. Seed germination requirements showed a relatively wide range of moisture conditions, but a narrow temperature range of 25-30℃. The optimum burial depth for seed germination was 10-15 mm. The seeds of C. mongolica can complete germination within 15 days when sown under suitable conditions. The water cycle had no significant effect on germination. The seeds buried in shallow soil were able to imbibe rapidly after full precipitation. (3) The most suitable temperature for seedling growth was approximately 25℃, although seedlings could tolerate a high temperature of up to 50℃ for a short period. Prolonged high or low temperature and frequent watering increased seedling death. The water cycle significantly influenced plant height and stem basal diameter. Shortening the water cycle can increase the height and stem thickness of C. mongolica. There was a significant influence of temperature on leaf age. The optimum temperature for leaf growth of C. mongolica was 25℃. Furthermore, variable temperature conditions were beneficial for erect growth and the thickening of stems. It was concluded that C. mongolica has relatively strict requirements for seed germination and seedling growth. The discrepancy between germination and seedling growth requirements narrowed the seedling establishment window. In the natural habitats of C. mongolica, the conditions are often not able to meet the requirements for the entire process from seed germination to seedling establishment. This is the main reasons for the relatively poor dispersion of C. mongolica populations through sexual propagation under field conditions.