Abstract: Achieving carbon neutrality is related to a complex giant system involving interwoven coupling and feedback of multiple systems including nature, society, economy, behavior, technology and energy. It faces many challenges such as cross-system and cross-sectoral coupling, sub-industry heterogeneity, technology cost dynamics, nonlinearity of technology and behavioral evolution, and social and economic uncertainties. To carry out the research of carbon emission technology planning under the constraint of carbon peak and carbon neutrality target, it is urgent to develop appropriate methods and models that can depict the connotation of the above challenges. To this end, this research designs and builds a bottom-up national energy technology model (named C³IAM/NET) from the perspective of complex system, by coupling the whole process including energy conversion, transportation, end-use consumption, recycling management and end treatment, and meanwhile coupling the whole industry chain including raw material, fuel, production process, technology and product/service. Finally, C³IAM/NET model fulfills the goal of production determined by demand, supply and demand interlinkage, and the coordination between technology and economy. C³IAM/NET model provides effective method and tools for the design of low-carbon transition pathway. C³IAM/NET model has been successfully applied to the optimization of carbon peak and carbon neutrality schedule and roadmap for China. But in order to facilitate the reading of different types of readers, the relevant content of the model application will be introduced in the sister article (Roadmap for achieving China’s Carbon Peak and Carbon Neutrality).