Drought is a major environmental factor limiting crop productivity. Photosynthesis is very sensitive to drought. Basic helix-loop-helix (bHLH) transcription factors (TFs) are important in response to abiotic stress. However, their functions remain unclear. Herein, we generated CgbHLH001 (a TF gene from halophyte Chenopodium glaucum)-overexpressed (OE) and ZmbHLH-RNA interference (Ri) maize lines to investigate their photosynthesis-associated indexes under drought conditions. The photosynthetic capacity was increased in OE lines under drought stress compared with that in non-transgenic (NT) and Ri plants. A greater root biomass, higher root/shoot ratio, and a relatively lower leaf area reduction ratio was also observed in OE plants. Compared to NT and Ri plants, OE lines showed a higher chlorophyll content and net photosynthetic rate and better chlorophyll fluorescence parameters under drought conditions. Fructose and glucose contents were also significantly elevated in OE lines. Moreover, under stressful conditions, CgbHLH001 overexpression increased the expression of genes related to photosynthesis. Transcriptomic data showed that many differentially expressed genes were enriched in the photosynthetic system in OE and Ri plants under drought conditions and were prone to being upregulated under drought stress in OE plants. Therefore, our results suggest that CgbHLH001 improves photosynthetic efficiency under drought stress and confers drought tolerance in maize seedlings.