The relationship between the starting and ending atomic layers of YBa2Cu3O7−x and Bi2Sr2CaCu2O8 thin films is studied by high‐resolution electron microscopy. Experimental results show that the starting atomic layer of the thin film is determined by surface chemistry and the interaction between the thin film and the substrate, while the ending layer of the thin film is thermodynamically determined by the high‐Tc cuprate itself. Therefore, nonunit cell nucleation is often observed in certain cases. The surface atomic layers of YBa2Cu3O7−x and Bi2Sr2CaCu2O8 were found to be the CuO layer and single BiO layer, respectively.