Cu(In,Ga)Se2 (CIGS) thin film solar cell has the advantages of high efficiency, good working stability and low manufacturing cost, which is the most promising thin film solar cell. Currently, the efficiency of CIGS thin film cell has reached 23.35% by doping alkali elements. This review summarized the current status of doping alkali elements on flexible CIGS thin film solar cells with a focus on recent advancements intended for higher efficiency and novel applications. First, the structure of CIGS thin film cell was introduced. According to the structural characteristics of CIGS cells, different doping methods of alkali metals were summarized. Then, the recent developments and trends of research in doping methods of alkali elements within the last years were reviewed, and the effect of different alkali elements on CIGS efficiency was emphasized. Finally, the challenges and opportunities of alkali doping CIGS solar cell were prospected.