Based on a long-term field experiment of greenhouse soil conducted for 11 consecutive years under different irrigation lower limits (W₁: 25 kPa, W₂: 35 kPa, W₃: 45 kPa, and W₄: 55 kPa), tomato was used as the test crop, and soil pH, exchangeable acidity, soil pH buffering capacity (pHBC), and other soil indicators of 0-50 cm soil layers were measured to investigate the effects of lower irrigation lower limits on the acidity characteristics of greenhouse soils. The results showed that pH of W₁ and W₄ showed a trend of initially decreasing and then increasing with the increase of soil depth, while pH of W₂ and W₃ gradually increased. Soil pH of each soil layer in W₂ and W₃ was significantly higher than that in W₁ and W₄. Soil pH buffering curves of each treatment showed that the surface changes were smaller than those of the deeper layers, and soil pHBC of each treatment showed a decreasing trend with the increase of soil depth. pHBC of W₂ increased by 7.76%-92.87% compared with other treatments. Soil exchangeable acidity showed a general decreasing trend with the increase of soil depth for all treatments, and the content of exchangeable H⁺ was much higher than that of exchangeable Al³⁺, being the main the dominant exchangeable acid component. Soil exchangeable acidity, soil exchangeable H⁺ and Al³⁺ contents under W₂ and W₃ were significantly lower than those in W₁ and W₄ in the same soil layers. In addition, W₂ increased the total exchangeable base cations and HCO- 3 content, enhancing the acid buffering performance. Correlation analysis further showed that both exchangeable H⁺ and Al³⁺ were significantly positively correlated with exchangeable acidity, but their changing trends were different. The growth rate of H⁺ content gradually decreased with the increase of exchangeable acidity, while the increase trend of Al³⁺ was the opposite. There was a significant negative correlation between soil pH and exchangeable acid content under different irrigation lower limits, with W₂ showing the smallest decrease in pH. Therefore, comprehensive consideration of soil buffering capacity, the relationship between pH and exchangeable acidity, irrigation lower limit of 35 kPa is the most suitable water management practice for greenhouse soils.