GeTe-Sb2Te3-based　superlattice　(GST-SL)　is　a　new　phase　change　film　prepared　with　alternative　GeTe　and　Sb2Te3　layers,　known　as　interfacial　phase-change　material,　showing　strongly　improved　switching　properties.　However,　the　recent　experiments　showed　that　Ge/Sb　atomic　intermixing　was　hardly　to　be　avoided　and　would　influence　the　phase　change　process.　In　this　paper,　the　effects　of　Ge/Sb　atomic　intermixing　on　the　local　structure　and　phase　change　mechanism　were　investigated　by　first-principles　simulations.　The　free　energy　evolution　with　temperatures　indicated　that　Ge/Sb　intermixing　is　helpful　for　phase　change.　The　bond　analysis　and　local　order　parameter　showed　that　no　obvious　structure　changes　happened　when　lower　than　1200　K,　and　there　were　almost　no　fourfold　Ge-tetrahedral　structures　even　when　quenched　from　1500　K,　different　from　the　traditional　GST　materials.　The　Ge/Sb　intermixing　and　its　ratios　can　not　only　influence　the　structural　transition,　but　also　play　a　vital　role　on　the　optical　properties.　These　findings　enrich　a　deep　understanding　of　Ge/Sb　intermixing　on　GST-SL　phase　changes.