Abstract: 【Objective】 This study aims to explore the effects of saline/alkali stress on the growth and development of new transgenic high-yield cotton at germination stage and seedling stage, and evaluate its saline/alkali tolerance. 【Methods】 In this project, transgenic Bn-csRRM2 high-yield cotton HN9311 and CCRI-12 (parent control) were used as study materials, the values and differences of growth and development related indexes were calculated and analyzed under saline stress (150 mmol/L NaCl) and alkali stress (70 mmol/L NaHCO₃). 【Results】 Except the number of true leaves and root/shoot, the other direct indexes of HN9311 at germination stage and seedling stage significantly decreased under saline stress and alkali stress when compared with those of CCRI-12; Except for relative hypocotyl length and relative germination index under alkali stress at germination stage, and relative root/shoot under alkali stress at seedling stage, the other relative indexes of HN9311 at germination and seedling stages were significantly lower than or equal to those of CCRI-12; The relative saline/alkali damage rates of HN9311 at germination stage were 27.00% and 21.00%, and those of CCRI-12 were 22.75% and 23.00%. The relative saline damage rate of HN9311was significantly higher than that of CCRI-12. 【Conclusion】 Saline/alkali stress has a significant inhibitory effect on the growth and development of HN9311 at germination stage and seedling stage. HN9311 is more sensitive to alkali stress at seedling stage when compared with saline stress, saline tolerance at germination stage and saline/alkali tolerance at seedling stage were lower than those of CCRI-12.