PALM imaging based on single molecule localization has developed rapidly in the past decades.Using PALM, the resolution of microscope has been increased to 2-25 nm. In this study, we find that there is a close relationship between the laser power density and the localization precision in PALM imaging. To explore this relationship ,we tested the most commonly used fluorescent proteins (FPs), including photoactivatable, photoconvertable, and photoswitchable FPs in PALM imaging. The results show that with the increase of the laser power density, the photon yield of most FPs firstly increased and then became saturated, and the background noise increased almost linearly. The analysis shows that with the increasing laser power density, the localization error first decreased, and then increased. Therefore, it is very important to select the appropriate laser power density in PALM imaging. How to improving the resolution of PALM imaging has been a hot research topic. The results in this study can guide researchers to select appropriate laser power density in PALM imaging to obtain images with high resolution.