Dietary sugar is the major energy source for mosquitoes, but its influence on mosquitoes' capability to transmit malaria parasite remains unclear. Here we show that Plasmodium berghei infection changes global metabolism of Anopheles stephensi with the most significant impact on glucose metabolism. Supplementation of glucose or trehalose (the main hemolymph sugar) to mosquito increases Plasmodium infection by alkalizing the mosquito midgut. The glucose/trehalose diets promote rapid growth of a commensal bacterium, Asaia bogorensis, which remodels glucose metabolism and consequently increases midgut pH. The pH increase in turn promotes Plasmodium gametogenesis. We also demonstrate the sugar composition from different natural plants influences A. bogorensis growth and Plasmodium infection is associated with their capability to expand A. bogorensis. Altogether, our results demonstrate that dietary glucose is an important factor that determines mosquito's competency to transmit Plasmodium and further highlight a key role for mosquito-microbiota metabolic interactions in regulating development of malaria parasite.