It is highly desirable to develop high-performance chemical sensors, especially those based on the fluorescence intensity enhancement (also known as "turn-on") sensing. It is the same and more challenging for lanthanide materials, on account of the difficulty to sensitize the metal-chromophores in a desired way. Herein, guided by a " second-sphere interaction " strategy, we synthesized a polyamine-derived hexa-carboxylate ligand (H 6 L) to fabricate the Tb( Ⅲ )-based metal-organic framework (MMCF-4) for "turn-on" sensing of methyl amine in aqueous environment with ultra-low detection limit and high turn-on efficiency . MMCF-4 features lanthanide nodes shielded in a nonacoordinate geometry along with a secondary coordination sphere that is densely populated with H-bond interacting sites. Through H-bond interactions on second-coordination sphere, nonradiative pathways were suppressed as a result of binding-induced rigidification of the ligand, thereby leading to luminescence enhancement. Such "remote" interacting mechanism involved in the "turn-on" sensing event was confirmed by single-crystal X-ray diffraction analysis of the guest@MMCF-4 and molecular dynamic simulation studies. For the first time, "turn-on" sensing of organic analytes in aqueous media was achieved via the rational design of both primary and secondary coordination spheres of Tb (III) in Ln-MOFs. Our study contributes a new and promising design strategy to achieve high-performance "turn-on" sensing for not only lanthanide MOFs, but also luminescent materials driven by other metal chromophores.