In　situ　and　real　time　monitoring　chemical　reactions　has　been　subjected　to　widespread　concern　in　many　areas.　Herein,　a　novel　and　efficient　SERS　platform　constructed　from　coating　mesoporous　ZrO2　(mZrO2)　interlayer　onto　an　Ag　core　and　subsequently　depositing　outer　Ag　nanoparticles　was　successfully　fabricated.　The　Ag@mZrO2@Ag　nanocomposite　exhibited　an　ultrahigh　SERS　sensitivity　as　well　as　remarkably　photocatalytic　property　assisted　by　a　plenty　of　Ag　nanoparticles　on　the　outer　surface　and　photoactive　mZrO2.　Experimental　results　proved　the　limit　of　detection　of　Cr(VI)　was　down　to　10−8　M　and　the　good　linearity　dependence　of　SERS　intensities　on　the　logarithm　of　concentration　(R2　=　0.93)　was　obtained.　Moreover,　a　simple　SERS　method　was　used　to　in　situ　monitor　the　photocatalytic　reduction　of　Cr(VI)　under　visible　light　(λ　>　420　nm).　In　addition,　as　practical　SERS　substrates,　Ag@mZrO2@Ag　nanocomposites　presented　outstanding　signal　reproducibility　and　remarkable　storing　stability.　As　a　consequent,　this　study　came　up　with　a　new　strategy　for　in　situ　monitoring　photocatalytic　reactions　and　will　be　possibly　utilized　in　chemical　sensing　and　ecological　restoration　in　the　future.　©　2022　Elsevier　B.V.