Against the backdrop of intensifying global climate change, the Paris Agreement has set temperature control targets, and countries worldwide have committed to carbon neutrality. To address the climate crisis, scientifically planning carbon reduction pathways and designing effective policies are critical. This chapter systematically explores the core technologies and theoretical frameworks for carbon reduction pathway design. First, it highlights the role of system optimization technologies, particularly integrated assessment models (e.g., DICE, RICE, C3IAM), which couple economic and climate systems to quantify emission reduction costs and climate losses, providing dynamic optimization pathways for policymaking. Second, it introduces the “time–space–efficiency–benefit” coordination theory, which optimizes policy design across four dimensions: time (balancing intergenerational equity and mitigation investments), space (coordinating global collective action with regional interests), efficiency (integrating government regulation and market mechanisms), and benefits (aligning economic development with emission reduction goals). This theory has been applied to China’s Climate Change Integrated Assessment Model (C3IAM), enabling bidirectional feedback between climate and economic systems to support multiscenario policy simulations. The chapter also reviews the development and applications of integrated assessment models, emphasizing their significance in international climate negotiations and national strategies. Ultimately, it underscores that scientific models and coordination theories enhance the rationality and effectiveness of carbon reduction policies, advancing global climate governance objectives.