Abstract: 【Objective】 To explore the effects of water-retaining agents on photosynthetic characteristics of bag-type compound sape peppers, and to evaluate the effects of different doses of water-retaining agents on photosynthetic indexes of peppers by using principal component analysis. 【Method】 In this test, Ruiba No. 5 was used as the test material, and the amount of the water-retaining agent was used as a variable. The leaf photosynthetic rate, stomatal conductance, intercellular CO₂ concentration, transpiration rate and water use efficiency were used to study the effects of different dosages of water-retaining agents on the diurnal variation of photosynthetic characteristics of bag-type compound sape peppers. 【Results】 The results showed that the addition of a water-retaining agent to the cultivation substrate helped to improve the photosynthetic characteristics of pepper leaves. The net photosynthetic rate of each treatment was a "double-peak" curve, and a "lunch break" phenomenon occurred at 14:00 In addition to the intercellular CO₂ concentration, various indicators showed an increasing trend with the increase in the amount of water retaining agent. According to the principal component analysis, the photosynthetic characteristics of the B₅ treatment (3 g/hole) the best. The photosynthetic rate 12.91 μmol/(m² · s), and the stomatal conductance 0.22 μmol/(m² · s). Intercellular CO₂ was 163.82 μmol/mol, transpiration rate was 5.37 mmol/(m² · s), and water use efficiency was 3.28 μmol/(m² · s). 【Conclusion】 In summary, the application of 3 g/hole water-retaining agent in the cultivation medium performed the best photosynthetic indexes of pepper.