Monoterpenes are important components of plant essential oils and have long been used as raw materials for spices and food flavorings. <italic>Litsea cubeba</italic> is an economically aromatic plant species, the fruits of which produce essential oil with monoterpenes as the dominant components. As a branch point of carbon flow in the methyl erythritol phosphate (MEP) biosynthesis pathway, 1-deoxy-D-xylo-5-phosphate reductoisomerase (DXR) is a key rate-limiting enzyme that catalyzes the MEP pathway’s second committed step. Therefore, <italic>DXR</italic> has become an effective regulation target to improve the biosynthesis of plant monoterpenes. In this study, we identified a <italic>DXR</italic> from <italic>L. cubeba</italic>, which was highly expressed in fruits and induced by darkness and MeJA. An enzyme assay showed that recombination LcDXR protein catalyzed DXP with NADPH as the cofactor. Transient overexpression of <italic>LcDXR</italic> significantly increased the content of monoterpenes in <italic>L. cubeba</italic>. Furthermore, <italic>LcDXR</italic>-overexpressing tobaccos were conducted and showed almost 5.9-fold increase in monoterpenes production, including limonene, α-pinene, eucalyptol, linalool, terpineol and camphor. Overexpression of <italic>LcDXR</italic> activated the metabolic flux of monoterpene biosynthesis through crosstalk and feedback mechanism. In addition, <italic>LcDXR</italic>-overexpressing tobaccos had no effect on phenotype of transgenic tobaccos. Our results demonstrate that <italic>LcDXR</italic> is a critical regulator of the monoterpene production in <italic>L. cubeba</italic> and other plants.