The quality of the perovskite film highly affects the performance of perovskite solar cells (PSCs). To deposit uniform and dense perovskite films, the fabrication processes are usually conducted in a controlled environment such as a glove box, which limits the future commercial development. High-quality perovskite films were fabricated in high humidity using mixed antisolvent consisting of ethyl acetate (EA) and diethyl ether (DE). It is found that the speed of perovskite crystallization could be controlled by adjusting the volume ratio of EA and DE in the mixed antisolvent, enhancing the grain size of perovskite films. The PSC fabricated in a humidity of 70% treated with an optimal ratio EA and DE exhibits an enhanced efficiency of 18.77% from 11.07%. Our work provides a convenient strategy for fabricating highly efficient PSCs in a high-humidity environment.