The goal of carbon neutrality opens the way for the deep decarbonization of the energy system. However, the exploration and development of domestic oil and gas resources continue to increase, so the development of oil and gas resources will become one of the key directions for the decarbonization of the energy system. The huge potential of CO2-EOR to enhance oil and gas recovery and realize CO2 geological storage has attracted much attention. The CO2-EOR projects have been carried out in China's Songliao, Bohai Bay, Ordos, and Jungeer Basins, etc. In this study, eight blocks of CO2-EOR in the Daqing, Changqing, Xinjiang, Jilin, Shengli, Zhongyuan and Jiangsu Oilfields and Yanchang Petroleum were selected. Based on the carbon emission analysis framework from the bottom-up engineering perspective, modeling stages including exploration, drilling and completion, extraction, treatment and transportation were included to analyze the trend of production carbon emissions from 2000 to 2021 in the oilfields, further to analyze the change of carbon intensity of CO2 flooding completely replacing water flooding under two technical scenarios: continuous CO2 injection and alternating water and gas injection. The results show that: (1) Due to the increase of energy demand caused by resource exhaustion, the carbon intensity of production in most oil fields showed a slow upward trend after 2000, and the total upstream carbon emission increased with increments of oil production from 2000 to 2014. In 2021, the total upstream carbon emission in 8 oil fields was 3,088,500 tonnes CO2eq. (2) Regardless of the scenario of either continuous CO2 injection or alternate water and gas injection, when the proportion of CO2 injection and sequestration is greater than 30%, the carbon intensity of production gradually changes from positive to negative, and it becomes an oilfield with net negative CO2 emission in the production process. As an important part of carbon capture, usage and storage (CCUS) technology, CO2-EOR technology will play a crucial role in the future decarbonization of oil and gas energy systems. The scale of trial, production and promotion of CO2-EOR projects should be further expanded in the future.