In order to explore the influence mechanism of biochar on baby cabbage yield and water and fertilizer utilization efficiency，the optimal amount of biochar for rain-fed and dry crop baby cabbage in the mountainous area of southern Ningxia was explored.With the Golden Queen as the test material，a randomized block test design was adopted，with a total of 8 treatments，and each treatment repeated 3 times.The effects of different treatments on the growth，yield and quality of baby cabbage，soil physical and chemical properties，soil enzyme activities，water and fertilizer use efficiency in rain-fed dry farming areas were analyzed.The results showed that without applying N fertilizer，the addition of 10 t·hm-2 of biochar had a greater impact on the cumulative value of the net photosynthetic rate of leaves.When adding 20 t·hm-2，the accumulation of dry and fresh matter in the underground part was the largest.When the biochar was added to 30 t·hm-2，it significantly increased the chlorophyll content in the later stage；on the contrary，applying N fertilizer and adding biochar 20 t·hm-2 was beneficial to the growth of baby cabbage，which significantly increased the soluble protein content and reduce nitrate content (524.63 mg·kg-1)，increased the weight per plant (1992.74 g)，net weight per plant (1431.33 g)，biomass (159.50 t·hm-2)，economic yield (114.56 t·hm-2) and water and fertilizer use efficiency (17.00%～56.31%).When biochar was added to 30 t·hm-2，soil physical and chemical properties，soil enzyme activity，soluble sugar content and vitamin C content of baby cabbage were all significantly increased.In summary，under the condition of combined application of nitrogen fertilizer，adding 20 t·hm-2 biochar can significantly reduce the nitrate content of baby cabbage in rain-fed dry farming in the mountainous area of southern Ningxia，improve the water and fertilizer use efficiency of baby cabbage，and realize water saving and efficiency.