Surface-enhanced　Raman　spectroscopy　(SERS)　is　a　powerful　tool　for　nondestructive　and　ultrasensitive　optical　trace-detection.　However,　the　sophisticated　fabrication　processes　and　performance　degradation　on　flexible　substrates　block　SERS　for　practical　uses.　Here,　we　report　a　facile　flexible　microsphere-coupled　SERS　(McSERS)　substrate　composed　of　a　dielectric　microsphere　cavity　array　(MCA)　and　random　gold　nanoparticles　(AuNPs)　capping　on　a　polydimethylsiloxane　(PDMS)　film　(MCA/AuNPs/PDMS)　for　giant　Raman　enhancement.　The　random　distribution　of　AuNPs　provides　a　hydrophilic　surface　against　to　the　coffee-ring　effect　for　uniform　localized　surface　plasmon　resonance　(LSPR)　response.　The　MCA　capped　on　the　AuNPs　boosts　the　Raman　intensity　via　the　multiple　optical　manipulation　processes,　in　which　the　photonic　nanojet　(PNJ)　confines　the　excitation　intensity　near　the　AuNPs,　whispering-gallery　mode　(WGM)　facilitates　the　energy　transfer　from　microsphere　cavities　to　AuNP　gaps　for　LSPR　boosting,　and　directional　antenna　effect　converts　near-field　Raman　signals　into　far-field　with　a　small　divergence.　Therefore,　the　Raman　scattering　is　dramatically　improved　with　the　enhancement　factor　(EF)　to　10(7)　for　the　limit　of　detection　(LoD)　of　4-nitrobenzenethiol　(4-NBT)　molecules　down　to　0.1　nM,　two　orders　of　magnitude　higher　via　MCA　coupling.　Moreover,　the　flexible　McSERS　substrate　exhibits　outstanding　durability　and　compatibility　as　an　ultrasensitive　Raman　test　strip,　by　which　the　thiram　concentration　is　detectable　down　to　2.42　ng/cm(2)　on　apple　peels.　The　present　work　provides　a　facile　strategy　to　fabricate　SERS　substrates　with　high　flexibility　for　optical　trace-detection　in　real-world　applications.