Accurate　detection　of　hydrogen　sulfide　(H2S)　in　live　cells　is　critical　for　understanding　its　role　in　disease　but　is　challenged　by　poor　biocompatibility,　signal　instability,　and　background　interference.　Here,　we　developed　a　novel　surface-enhanced　Raman　scattering　(SERS)　hydrogel　platform　based　on　carboxymethyl　cellulose-silver　nanoparticles　embedded　in　agarose　(CMC-Ag　NPs-AG).　This　platform　is　prepared　via　simple　physical　crosslinking,　enabling　uniform　Ag　NP　dispersion　and　stable　encapsulation.The　hydrogel　shows　excellent　swelling　capacity,　antibacterial　activity　(＞99　%　inhibition),　and　high　biocompatibility　(＞98　%　cell　viability).　Leveraging　the　specific　formation　of　Ag2S　upon　H2S　exposure,　the　platform　enables　ultrasensitive　and　selective　detection.　It　exhibits　a　wide　linear　range　(0.15-600　mu　M),　a　low　detection　limit　of　0.15　mu　M,　and　excellent　reproducibility　(RSD　=　1.10　%).　It　also　demonstrates　strong　anti-interference　performance　against　structurally　similar　sulfur-containing　molecules.Furthermore,　this　platform　was　successfully　applied　to　monitor　endogenous　H2S　in　A549　cancer　cells　under　varying　culture　conditions.　The　results　confirm　its　potential　for　real-time,　in　situ　detection　of　gaseous　signaling　molecules　in　complex　biological　environments.　This　work　offers　a　robust　and　biocompatible　SERS　strategy　for　H2S　analysis　and　provides　new　insights　into　tumor　metabolism　and　disease　diagnosis.