An　enhancement　on　thermoelectric　performance　of　Cu2GeSe3　via　simultaneously　Ag-alloying　on　Cu　sites　and　Ga-doping　on　Ge　sites　is　achieved.　The　relatively　high　solubility　(similar　to　10%)　of　Ag　on　Cu　sites　allows　for　the　strong　point　defect　scattering　for　phonons,　which　causes　remarkable　reduction　in　lattice　thermal　conductivity.　Ag-rich　precipitates　emerge　when　the　amount　of　Ag　is　higher　than　the　solubility　on　Cu　site,　which　however　do　not　have　significant　effect　on　the　lattice　thermal　conductivity　since　it　is　already　very　close　to　the　lower　limit　of　kinetic　theory.　Ga-doping,　an　effective　way　to　tune　the　hole　concentration,　leads　to　optimization　of　power　factor　in　the　whole　temperature　range.　The　maximal　zT　obtained　in　Cu1.9Ag0.1Ge0.997Ga0.003Se3　is　1.03@786　K,　about　58%　higher　than　that　in　previous　report.　In　addition,　the　average　zT　in　the　temperature　range　from　320　K　to　786　K　is　0.58,　implying　great　potential　for　fabrication　of　thermoelectric　devices.　(c)　2018　Elsevier　B.V.　All　rights　reserved.