Spodoptera litura is a voracious pest in tobacco fields, while Eocanthecona furcellata, as its dominant predatory natural enemy, exhibits significant potential in pest control. Evaluating the sublethal effects of the novel insecticide broflanilide on both species is crucial for achieving synergistic chemical-biological control of S. litura. In this study, the leaf dip method was employed to determine the toxicity of four chemical insecticides, including broflanilide, against the 3^rd instar larvae of S. litura. The sublethal dose (LC₃₀) of broflanilide was applied via spray treatment to investigate its impacts on the developmental duration, food consumption, and fecundity of the parental (F₀) and offspring (F₁) generations of S. litura. Concurrently, the effects of this insecticide on the lifespan, oviposition parameters, and of offspring nymphs survival rate of E. furcellata female adults were analyzed. Results showed that the LC₃₀ of broflanilide against S. litura was 0.004 mg/L. Spray treatment with this sublethal concentration significantly prolonged the developmental duration of 3^rd-6^th instar larvae in the F₀ generation, reduced the daily food consumption and total fecundity of 3^rd-6^th instars. In the F₁ generation, the total developmental duration was prolonged by 2.21 days, and fecundity decreased by 31.6%. For E. furcellata female adults, this treatment prolonged the pre-oviposition period by 6.33 days, reduced total fecundity by 54.19%, and decreased oviposition frequency by 4.00 times, while showing no significant effects on adult lifespan, offspring survival rate, or developmental duration. This study clarifies the sustained control potential of broflanilide against target pests and the sublethal impacts on the reproduction of E. furcellata, providing a theoretical basis for optimizing pesticide application strategies and protecting predatory natural enemies.