CsPbBr3‐based perovskite solar cells possess both high humidity and temperature tolerance, and also have excellent long‐term stability in air, but the defect states in the bulk perovskite are always an obstacle for further improvement of their efficiency. Herein, a doping strategy is demonstrated in which AgBr is directly added to the precursor solution in the first step. An appropriate amount of Ag+ ion doping can passivate the defects in bulk or at grain boundaries, reduce the defect density of the film, and form a pinhole‐free film. Finally, the best power conversion efficiency of the solar cell reaches to 6.92% and exhibits a long‐term stability in a humid environment. This work provides a simple and effective method for improving the quality of CsPbBr3 film and the performance of CsPbBr3‐based perovskite solar cells.