A sequential route for low-cost fabrication of high quality Ag-alloyed CIGS absorbers is reported. Ag-alloying is introduced into the CuInGa precursor to widen the band gap and improve the crystallinity of the ACIGS absorbers. The morphological, compositional, and structural characteristics of the ACIGS absorber are also systematically investigated. Different Ag thin layer incorporation locations at the bottom, in the middle and on the top of CuInGa precursors are schemed for deep understanding the band gap energy and crystallinity regulation mechanism of Ag alloying. A conversion efficiency of 10.2% is achieved for the ACIGS device with Ag at the bottom. The notable Voc improvement can be obtained due to the widened band gap and the band gap gradient in the absorber created by the Ag and Ga elements grading. Finally, the ACIGS absorbers are further sulfurized and a highest power conversion efficiency of 13.01% is obtained. Our results indicate that the sequential magnetron sputtering is a promising way for the fabrication of CIGS thin film solar cells.