Polyethylene glycol (PEG) is widely used in copper plating as an inhibitor. The PEG-Cu+-Cl structure is recognized as the dominant factor in the inhibition mechanism of PEG. In this work, we investigated the influence of temperature on the PEG-Cl inhibition system. Molecular dynamic (MD) simulations based on Density Functional Theory (DFT) were employed to examine the influence of temperature on the adsorption of Cl− on copper surface and the structure of PEG-Cu+-Cl. According to the MD results, it is assumed that there is a negative correlation between the inhibition effect of PEG and the working temperature. The results of corresponding electrochemical measurements are in good agreement with this assumption and the surface morphology analysis of plated copper films confirms this correlation.