Sclerodermus guani Xiao et Wu, 1983 plays a significant role in the biological control of agricultural and forestry pests. To investigate whether different sugar types significantly affect the longevity, fecundity, and nutrient reserves of female S. guani adults, this study provided 1 mol/L solutions of sucrose, fructose, glucose, mannose, or trehalose under laboratory conditions, with a distilled water group serving as the control. The longevity and nutrient content of parasitoids were measured after varying feeding durations, while fecundity was assessed in preliminary experiments. The results demonstrated that prolonged sugar feeding significantly extended parasitoid longevity, with fructose, glucose, and sucrose exhibiting the most pronounced effects and no significant differences among them. Nutrient analysis revealed that sugar consumption significantly increased total carbohydrate content, slowed lipid depletion, and promoted protein accumulation. Sucrose, fructose, and glucose outperformed other sugars and the control in these aspects. Fecundity assays indicated that glucose and trehalose significantly shortened the pre-oviposition period and enhanced egg production. In conclusion, nutritional supplementation markedly improves the longevity and reproductive performance of S. guani, with 1 mol/L glucose identified as the optimal dietary source.