We　report　a　line　excitation　scheme　for　surface　enhanced　Raman　scattering　(SERS)　using　a　graphene　substrate　deposited　with　silver　nanoparticles　(AgNPs).　Direct　laser　writing　was　employed　for　producing　laser-induced　graphene　(LIG)　layer　on　polyimide　and　electrochemical　reaction　was　used　to　grow　AgNPs　onto　the　surface　of　LIG.　In　addition　to　the　local-field　enhancement　on　the　plasmonic　hotspots,　the　graphene-based　charge-transfer　and　molecular　adsorption　properties　make　further　contributions　to　the　SERS　mechanisms.　Compared　with　conventional　point　excitation,　the　line　excitation　scheme　allows　much　extended　dynamic　range　of　the　excitation　laser　power　before　reaching　the　damage　threshold　of　the　target　molecules,　much　enhanced　Raman　signal　due　to　the　integration　over　the　focusing　line,　and　high　reliability/repeatability　of　the　SERS　signals.　This　also　reduces　significantly　the　sensitivity　of　the　SERS　signals　to　the　randomly　distributed　nanostructures.　Thus,　much　enlarged　excitation　area/volume　for　Raman　interactions　enables　high　stability　of　the　signals　with　multiplied　intensity　through　integration　over　the　focusing　line,　as　compared　with　point　excitation　scheme　under　the　same　excitation　power　density.　The　line　excitation　scheme　shows　a　detection　limit　of　100　ppb　in　tracing　melamine　in　water,　attaining　an　enhancement　factor　of　larger　than　100,　as　compared　with　point　excitation.