Nanoscale thin-film composite (TFC) polyamide membranes are highly desirable for desalination owing to their excellent separation performance. It is a permanent pursuit to further improve the water flux of membrane without deteriorating the salt rejection. Herein, we fabricated a high-performance polyamide membrane with nanoscale structures through introducing multifunctional crown ether interlayer on the porous substrate impregnated with m-phenylenediamine. The crown ether interlayer can reduce the diffusion of amine monomers to reaction interface influenced by its interaction with m-phenylenediamine and the spatial shielding effect, leading to a controlled interfacial polymerization (IP) reaction. Besides, crown ether with intrinsic cavity is also favorable to adjust the IP process and the microstructure of polyamide layer. Since the outer surface of the nanocavity is lipophilic, crown ether has good solvency with the organic phase, thus attracting more trimesoyl chloride molecules to the interlayer and promoting the IP reaction in the confined space. As a result, a nanoscale polyamide membrane with an ultrathin selective layer of around 50 nm is obtained. The optimal TFC polyamide membrane at crown ether concentration of 0.25 wt.% exhibits a water flux of 61.2 L·m⁻²·h⁻¹, which is 364% of the pristine TFC membrane, while maintaining a rejection of above 97% to NaCl. The development of the tailor-made nanoscale polyamide membrane via constructing multifunctional crown ether interlayer provides a straightforward route to fabricate competitive membranes for highly efficient desalination.