To meet the challenge of global climate change and sustainable development in the energy sector， the power system CO2emission structure and influencing factors are analyzed. Based on an incremental analysis， the structure identification and evaluation method of power system CO2emission is proposed. According to the emission structure， the calculating method of the low-carbon contribution of each influencing factor and the contribution to the15% non-fossil energy consumption in 2020” goal of China are established as well. As the verification of the effectiveness of the method proposed， a case study of Guangdong province is presented.