CaKFe4As4 is a new-type superconductor with a relatively high transition temperature of 35 K among stoichiometric iron-based superconductors.Based on scanning tunneling microscopy/spectroscopy,the surface morphology and electronic structure of CaKFe4As4 single crystal were systematically investigated.The cleaved CaKFe4As4 showed various morphologies,such as atomically resolved 1 × 1,1 ×2,and √2 × √2 lattices.By analyzing the geometrical correlations of these morphologies,the 1 × 1 and 1 ×2 lattices were identified as the original and reconstructed As layers,respectively,whereas the √2 × √2 lattice was distinguished as the reconstructed alkaline-earth-metal or alkali-metal layer.The superconducting energy gap of 7.3 meV and bosonic mode of 12.7 meV were resolved in the scanning tunneling spectra.In addition,the superconducting energy gaps measured on different terminations were identical and consistent with the values obtained by bulk-sensitive techniques,in-dicating that the electronic structures of CaKFe4As4 were insensitive to the surface reconstructions.Our study clarifies the relationships between complex surface reconstructions and surface terminations and preliminarily presents that there is no obvious effect of surface reconstructions on electronic states.