In　this　paper,　the　effects　of　Nb　addition　on　the　mechanical　properties,　electrical　conductivity　and　microstructure　of　the　Cu-Ni-Si-Mg　alloy　were　investigated.　The　results　show　that,　after　the　secondary　aging　at　460　degrees　C　for　120　min,　the　alloy　with　0.2　wt%　Nb　exhibits　the　best　comprehensive　properties　with　a　hardness　of　245.9　HV,　a　tensile　strength　of　747.28　MPa,　a　breaking　elongation　of　8.6%,　and　an　electrical　conductivity　of　47.74　%IACS.　The　addition　of　Nb　element　can　promote　the　precipitation　of　Ni2Si　phase.　The　Nb-doped　alloy　has　a　higher　quantity　of　precipitates　and　a　smaller　size　of　precipitates.　The　Nb　element　promotes　the　transition　of　the　Ni2Si　phase　from　a　coherent　to　an　incoherent　relationship　with　the　matrix　in　the　Cu-Ni-Si-Mg　alloy.　In　the　initial　stage　of　precipi-tation,　the　precipitation　activation　energy　of　the　alloy　with　0.2　wt%　Nb　is　46.86%　lower　than　that　of　the　alloy　without　Nb.　The　addition　of　Nb　increases　the　proportion　of　sigma　3n　(n　=　1,　2,　3)　grain　boundary　in　the　Cu-Ni-Si-Mg　alloy.　Furthermore,　after　the　secondary　aging,　the　Nb　addition　increases　the　recrystallized　texture　and　recrys-tallized　grains　and　decreases　the　cold-rolled　texture　and　defects　in　the　alloy.