Two-step sequential deposition of CH3NH3PbI3 (MAPI) films is widely used in the preparation of perovskite solar cells, but still suffers from some drawbacks such as residual PbI2 and uncontrollable surface morphology of MAPI films. Here a modified two-step sequential deposition is reported to prepare MAPI films with pure phase and smooth surface. The process involves the deposition of a low-crystallinity PbI2 film firstly and subsequent spraying of CH3NH3I solution. A well-converted and extremely surface-smooth MAPI film was successfully prepared via this two-step method. The weak crystallinity of raw PbI2 film leads to the pure MAPI film. The following spraying of CH3NH3I solution in a spin-coating process results in MAPI films with much smoother surface, better crystallization and higher absorption compared with the traditional method of immersing in CH3NH3I solution. Consequently, the corresponding mesostructured perovskite solar cells based on these MAPI films achieve a high efficiency of 14.3% and good reproducibility, which demonstrates the advantages and promising applications of this modified two-step sequential deposition method.