Transition metal dichalcogenide (TMDC) nanomaterials have become excellent candidates for next-generation functional membranes. In the past few years, tremendous encouraging experimental and theoretical studies have been conducted on TMDC-based nanomaterials, which opened up a new direction for developing highly selective and permeable membranes. Herein, we systematically summarize the recent advances in 2D TMDC nanomaterials and their application in water purification. The physical and chemical properties of TMDC-based functional membranes that facilitate water purification are stated in detail. Simultaneously, the theoretical investigations used to understand the desalination process of the TMDC-based membranes are also summarized. Furthermore, we sum up the synthesis method and discuss the modification strategies for TMDC-based membrane in water purification application. Finally, the challenges and perspectives on the future development of TMDC-based functional membrane for water purification, as well as the future research direction for functionalization of TMDC-based membrane, are proposed.