Based　on　the　photovoltaic　properties　and　tandem　solar　cells　theory,　Gallium　Indium　Arsenide/Germanium　Stannide　(GaInAs/GeSn)-based　double-junction　(DJ)　solar　cells　have　been　numerically　simulated　for　the　first　time.　In　this　study,　we　explore　the　band　gap　combination　under　lattice　matching　and　obtain　the　content　of　In/Sn　at　optimal　efficiency,　which　is　expressed　as　Ga0.84In0.16As/Ge0.93Sn0.07　DJ　solar　cell　(1.20/0.58　eV).　Afterward,　it　is　optimized　in　terms　of　variation　in　the　doping　contents　and　active　layer　thickness.　To　take　full　advantage　of　the　electron　mobility　of　the　material,　the　optimal　＇inverted　doping　profile＇　concentration　N　(a(d))　is　1.5(5)/5(20)　x　10(18)　cm(-3).　In　addition,　the　reasonable　p(n)　layer　thickness　could　be　comprised　of　0.2-0.8(0.2-1)/0.5-3(1-4)　&　mu;m　of　the　DJ　solar　cells　with　less　material　consumption.　When　the　p(n)　layer　thickness　is　0.30(0.25)/0.9(1.35)　&　mu;m,　the　tandem　device　can　achieve　an　optimal　efficiency　of　31.00%　with　28.98　mA　cm(-2)　(J　(sc)),　1.25　V　(V　(oc))　and　85%　(FF).　This　study　highlights　that　GeSn　materials　have　the　potential　to　combine　with　III-V　materials　to　form　low-cost　and　high-efficiency　tandem　devices.