Carbon emission peak and neutrality prospect has expedited the revolution of conventional energy utilization mode, particularly in highly energy-intensive industries. The petrochemical industry bears great responsibility for energy conservation and carbon emission reduction. TES (Total Energy System) retrofit schemes in the petrochemical industry classified as REST (Retrofitting through Energy-Saving Techniques) and RSFC (Retrofitting through Substituting Fossil fuel with Clean energy) have emerged in large numbers recently. It is challenging for energy managers to optimize and assess TES retrofit schemes simultaneously and globally, once clean energy supply is involved. State-of-the-art assessment and optimization method for TES retrofitting is urgently needed. This work proposes a novel optimization and assessment method based on the exergy conversion and consumption processes to figure out the most cost-effective retrofit schemes in view of exergy analysis. The method features with the simulation of TES, the clean energy substitution for fossil fuel, the optimization of the subsystems, and the exergy efficiency assessment of retrofit schemes. The double-parallel-loop application framework is then presented, which deals with the optimization and assessment of RSFC and REST simultaneously. Combined plants of continuous catalytic reforming and aromatic extraction plants along with their matched TES are investigated. A MINLP optimization model is formulated and programmed with GAMS software. The optimal results show that the total exergy consumption decreased by 3200 kW with clean energy substitution. Sensitivity analysis explores the energy conservation benefits and exergy efficiency improvement when clean energy with different qualities and quantities substituting for fossil fuel, which provides valuable information for feasibly implementing retrofit schemes. Comparison of scenarios reveals the interacting influence between the implementation of RSFC and REST, which is significant for decision-making when multiple retrofit schemes are alternatives. Real-world case investigations demonstrate the validation and efficacy of the proposed method. The main findings of this study are significant and quantitative references for petrochemical industrial practice, which would contribute to energy conservation and carbon emission reduction in the future.