[Objective] Ectropis obliqua Prout (Lepidoptera:Geometridae) is the most devastating insect pest of tea plants in China. Studying on the relationship among feed, gut microbial flora and fitness of Ectropis obliqua is of relatively high theoretical value for the management of E. obliqua. [Methods] We analyzed the effect of artificial diet (without tea ingredients) and tea leaves on survival of Ectropis obliqua larvae. We also analyzed the similarities and differences of gut microbial flora in Ectropis obliqua larvae fed with different feeds based on high-throughput sequencing technology. [Results] The mortality of larvae were significantly different. Larvae fed with artificial diet had high mortality. Larvae fed with artificial diet had higher bacterial diversity and evenness than larvae fed with tea leaves. Many bacteria were found in the gut of Ectropis obliqua larvae. [Conclusion] Feed affects the survival and the gut microbial flora of Ectropis obliqua larvae.