The　structural　and　electronic　properties　of　Pt-4　nanoparticles　adsorbed　on　monolayer　graphitic　carbon　nitride　(Pt-4/g-C3N4),　as　well　as　the　adsorption　behavior　of　oxygen　molecules　on　the　Pt-4/g-O3N4　surface　have　been　investigated　through　first-principles　density-functional　theory　(DFT)　calculations　with　the　generalized　gradient　approximation　(GGA).　The　interaction　of　the　oxygen　molecules　with　the　bare　g-C3N4　and　the　Pt-4　clusters　was　also　calculated　for　comparison.　Our　calculations　show　that　Pt　nanoparticles　prefer　to　bond　with　four　edge　N　atoms　on　heptazine　phase　g-C3N4　(HGCN)　surfaces,　forming　two　hexagonal　rings.　For　s-triazine　phase　g-C3N4　(TGCN)　surfaces,　Pt　nanoparticles　prefer　to　sit　atop　the　single　vacancy　site,　forming　three　bonds　with　the　nearest　nitrogen　atoms.　Stronger　hybridization　of　the　Pt　nanoparticles　with　the　sp(2)　dangling　bonds　of　neighboring　nitrogen　atoms　leads　to　the　Pt-4　clusters　strongly　binding　on　both　types　of　g-C3N4　surface.　In　addition,　the　results　from　Mulliken　charge　population　analyses　suggest　that　there　are　electrons　flowing　from　the　Pt　clusters　to　g-C3N4.　According　to　the　comparative　analyses　of　the　O-2　adsorbed　on　the　Pt-4/HGCN,　Pt-4/TGCN,　and　pure　g-C3N4　systems,　the　presence　of　metal　clusters　promotes　greater　electron　transfer　to　oxygen　molecules　and　elongates　the　O-O　bond.　Meanwhile,　its　greater　adsorbate-substrate　distortion　and　large　adsorption　energy　render　the　Pt-4/HGCN　system　slightly　superior　to　the　Pt-4/TGCN　system　in　catalytic　performance.　The　results　validate　that　being　supported　on　g-C3N4　may　be　a　good　way　to　modify　the　electronic　structure　of　materials　and　their　surface　properties　improve　their　catalytic　performance.