The catalytic mechanism of HFC-245fa on clean and O atom pre-adsorbed Cu(1 1 1) surfaces are investigated by using Density Functional Theory (DFT) calculation. Six initial dissociation reaction pathways of HFC-245fa on clean and O atom pre-adsorbed Cu(1 1 1) surfaces and the related homolytic reactions of HFC-245fa molecule via initial C-F, C-H and C-C bonds breakages are investigated, respectively. The reaction energies, energy barriers, and bond dissociation energies are calculated and compared to investigate the catalytic mechanism of HFC-245fa on clean and oxygen atom pre-adsorbed Cu(1 1 1) surfaces, this result shows that while the energy barriers of C-F bond and C-H bond decomposition pathways in HFC-245fa on the clean Cu(1 1 1) surface are much smaller than the corresponding bond dissociation energies in the homolytic reactions of HFC-245fa molecule, the breakage energy barriers of C-C bond are comparable in these two cases. The energy barriers of all initial decomposition reaction pathways for HFC-245fa on clean Cu(1 1 1) surface are higher than that of HFC-245fa on O atom pre-adsorbed Cu(1 1 1) surface. It is indicated that the Cu(1 1 1) surface can effectively catalyze the scission reactions of HFC-245fa and the O atom can facilitate these dissociation reactions. When the temperature of heat source is close to the decomposition temperature of HFC-245fa, copper used in the components of ORC system (such as evaporator) which works in the higher temperature, should be avoided, because copper can catalyze the decomposition of HFC-245fa.