Net Zero Energy Building (NZEB) has become an important development direction in the field of urban regeneration driven by the global carbon neutrality goal. This study takes Shenzhen and Guangzhou as the research objects to explore the differences and synergistic paths of the application of digital platforms in the building optimization strategy of Net Zero Energy Building (NZEB) urban renewal. Through literature analysis, case studies, field research, and data modeling, the study finds that: Shenzhen, with the advantage of policy advancement and technological innovation, is outstanding in the fields of photovoltaic integration and smart grids; while Guangzhou, with the experience of historical urban renewal and climate-adaptive design, is more distinctive in passive energy saving and community synergy optimization. The digital platform significantly improves the efficiency of energy forecasting, system integration and user behavior optimization in both places through BIM (Building Information Modeling), Internet of Things (IoT) and big data analysis. Empirical data shows that a zero-energy community renovation project in Shenzhen achieved an annual energy self-sufficiency rate of 112% by optimizing the design through the digital platform, while a historic district renovation project in Guangzhou reduced air-conditioning energy consumption by 30% through climate-adaptive algorithms. The study suggests that the two regions need to strengthen technical complementarity and data sharing, build a regional standard system for zero-energy urban renewal, and promote the application of digital platforms in cross-scale synergy, so as to provide a practical model for achieving the goal of carbon neutrality.