Abstract: To evaluate non-lethal effects of insecticide on pests completely, sub-lethal dose imidacloprid and population crowding were chosen as treatments. Reproduction, life span for soybean aphid adults, developmental periods of nymphs and number of alate aphids were measured to assess how would the two treatments effect on the pest population reproduction ability and risk of transfer on the host plants. The results showed that sub-lethal dose of imidacloprid significantly reduced reproduction rate of soybean aphid, thus effectively reducing the local damage on soybean seedling. In addition, the number of winged aphids decreased significantly, which could reduce the risk of aphids transfer accordingly. Moreover, crowding treatment reduced fecundity of the first generation aphid, but had no significant effect on the fecundity of the second generation. Crowding increased the number of winged aphids which would increase the risk of aphids transfer. Statistics also revealed that there was a significant interaction between pesticide and congestion. Based on above experiments, sub-lethal dose of imidacloprid can effectively control local damage and transfer damage of soybean aphid progenies on the original plant. Congestion will reduce the damage control effect of the pesticide on the aphids, furthermore, increase the risk of aphid transfer.