The biggest challenge for the pursuit of potentially available organic-inorganic perovskite solar cell is to achieve both high power conversion efficiency and good long-term stability. Here, the trimesic acid is first used as an additive in the lead precursor solution to prepare perovskite film by a two-step solution method to improve the performances of perovskite solar cell. After adding trimesic acid into the lead precursor, the device efficiency is increased from 14.27% to 17.21% and the device stability is improved. This can be attributed to the improvement of crystal structure and quality of perovskite film. The results indicate that the use of trimesic acid additive by a two-step solution is a great way to design high-efficiency and stable perovskite solar cells.