The work aims to study the influence of Ag doping on the phase composition and thermoelectric properties of Cu2Se thin films. Ag-doped Cu2Se thermoelectric thin films were deposited by high vacuum magnetron sputtering using a powder sintered Cu2Se alloy target. The influence of Ag doping on the phase composition and thermoelectric properties of the Cu2Se thin films were studied in this paper. The phase composition, surface morphologies, fracture cross-sections, micro-area element contents and element distribution of the thin films were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS). The thermoelectric properties of the Cu2Se films with different Ag contents were studied by measuring the resistivity and Seebeck coefficient by Seebeck coefficient/resistance analysis system LSR-3. The results show that the use of magnetron sputtering technology and α-Cu2Se alloy target can prepare Cu-Se thin films with β-Cu2Se phase as the main phase and a very small amount of α-Cu2Se phase. The Ag atom doped in the films does not enter the lattice of the β-Cu2Se phase, but forms a nano-sized CuAgSe second phase in the films. The β-Cu2Se phase lattice of the deposited films is rich in Cu. When the Ag content increases from 0 to 2.97at%, the ratio of [Cu]/[Se] in the β-Cu2Se phase lattice is more than the ideal ratio of 2.0, enhancing from 3.59 to 4.96.The resistivity of the deposited β-Cu2Se films is significantly lower than that of bulk materials in the literature due to Cu-rich in β-Cu2Se phase lattice. With the increase of Ag content, the resistivity of the deposited β-Cu2Se films decreases first and then increases; the Seebeck coefficient of the films increases with resistivity. The sample with Ag content of 1.37at% has the highest power factor due to the significantly higher Seebeck coefficient. The Cu-rich β-Cu2Se films prepared by magnetron sputtering has low resistivity, and the appropriate amount of Ag-doping can significantly increase the absolute value of the Seebeck coefficient, thereby obtaining a higher power factor.