Layered transition metal dichalcogenides (TMDs), such as MoS₂, WS₂, MoSe₂, WSe₂, etc., have received considerable interest recently due to their unique properties and fascinating applications. In this work, we proposed a NaCl template-assisted in situ chemical vapor deposition (CVD) strategy for synthesizing high-quality two-dimensional (2D) WS₂, MoS₂, MoSe₂ and WSe₂ nanosheets with a single-crystalline structure on a large scale. During the synthesis, 3D self-assembly of cubic NaCl particles can not only provide smooth surfaces to support the lateral growth, but also create a 2D confined space to restrict the thickening of TMD nanosheets, while the high-temperature annealing during the CVD process ensures high crystallinity and structural stability as well as remarkably promoting the conductivity of the TMD nanosheets. When evaluated as sodium-ion battery anodes, the representative WS₂ nanosheets exhibited a high reversible specific capacity of 453 mA h g⁻¹ at a current density of 0.1 A g⁻¹, an excellent cycling performance and a greatly enhanced rate capability. The charge storage mechanism together with the microstructure evolution of WS₂ nanosheets during the sodiation/disodiation processes is responsible for their superior sodium storage performance.