Abstract: The Central Committee of the Communist Party of China and the State Council issued the Opinions on Deepening the Battle Against Pollution Prevention and Control. The document clearly states that Greenhouse Gases (GHGs) control should be integrated into the Environmental Impact Assessment (EIA) management process. The notice pointed out that incorporating GHGs control into EIA has become an important initiative to further promote the carbon peaking action. Industrial parks are important carriers for controlling incremental emissions of pollutants and GHGs and promoting reduction of pollution and carbon at source. The key question of the research is to optimize planning options for reducing pollution and carbon emissions in a synergistic manner. Taking a petrochemical park as an example, the technical methods of GHGs assessment during the Planning Environmental Impact Assessments (PEIAs) of industrial parks are discussed. As part of the scientific and rational analysis and evaluation of GHGs emissions reduction potentials in EIAs, this study explores two technical approaches and their roles of GHGs evaluation on planning optimization and adjustment. First, a comprehensive assessment method for GHGs emissions and the atmosphere is proposed, and energy efficiency analysis of key emission facilities for GHGs assessment is carried out to combine the requirements of air quality improvement target in atmospheric assessment with the preliminary simulation results. The joint proposal recommends changes to the planning system to phase out inefficient and energy-intensive heat source facilities, and replace them with clean energy in stages. Secondly, study and innovate the PEIA method that closely combines GHGs assessment and circular economy analysis, follow the integrated design concept of chemical industry parks of collaboration, cooperation, and sharing, promote a circular economy to reduce carbon emissions through resource reuse and improved energy efficiency. Making full use of the natural advantages of carbon sequestration and carbon offset in the chemical industry parks to promote the synergy between industrial chains in the parks and achieve the maximum utilization of CO₂ resources and gradient utilization of energy in parks. The empirical study shows that: (1) Comprehensively identify the key links of pollution emission reduction and carbon emission reduction in the industrial park, focusing on improving efficiency and coal control, the integrated heat source plan is jointly proposed through the GHGs assessment and atmospheric assessment. Focusing on CO₂ resource utilization and energy gradient utilization in the industrial park, we have promoted the implementation of CO₂ recycling in six sets of units of two enterprises. It also implements CO₂ industry chain utilization projects such as polycarbonate and vinyl carbonate to consolidate the waste heat resources of dispersed enterprises into a network to maximize the use of waste heat and pressure. The application of this method proves the feasibility of the aforementioned technical methodology and the role of GHGs assessment in the optimization and adjustment of energy planning programs and circular economy programs in the industrial sector. (2) We adopt the whole-process incorporation model and propose a technical framework for whole-process evaluation of GHGs based on the evaluation technical process of the current EIA for industrial parks: ‘exploring potential’ in the evaluation of current situation, ‘integration of ideas’ in planning analysis, ‘setting target’ in the impact identification, ‘evaluating trend’ in the impact evaluation, ‘clarifying measures’ in the validation of scheme, and ‘optimizing scheme’ in the adjustment suggestions. Furthermore, this study provides an outlook for future research in the following areas. First, it is necessary to enhance synergy between pollution prevention and climate governance. Second, the focus should be placed on new emission sources and non-CO₂ GHGs that are difficult to quantify. Thirdly, differentiated GHGs emission reduction programs will be developed to meet the energy transition and environmental targets faced by each industrial park. Consequently, the technical framework and evaluation methods proposed in the study provide a strong basis for optimizing the source control role of EIA in chemical parks and have great practical relevance.