The small brown planthopper (SBPH) is a destructive agricultural pest, which causes economic losses to various crops, including rice, corn, wheat, and oats. Triflumezopyrim (TFM) is a new mesoionic insecticide used to control SBPH in China. However, the sublethal effects of TFM on the growth and fecundity of SBPH are unknown and require further study. In this study, the age-stage life table and physiological parameters were used to assess the TFM's sublethal effects on SBPH. We found that sublethal doses of TFM significantly changed the life table parameters of SBPH. The oviposition and fecundity of female SBPH decreased significantly after treatment with different sublethal doses, as did the emergence rate of adults. In contrast, insects treated with sublethal doses of TFM had longer developmental durations and adult life spans than the control group. The activities of carboxylesterase (CarE) and glutathione-S-transferase (GST) in the treatment group showed inhibitory effects. Mixed-function oxidase (MFO) showed an induction effects at 24 and 48 h after treated. The results showed that the sublethal doses of TFM had negative effects on the population development of SBPH. These results can provide a theoretical basis for population control and resistance management.