With increasing global energy constraints and stricter carbon emission targets, building operations account for 44.8% of total energy consumption. Enhancing the efficiency of heating and cooling load responses is essential for achieving carbon neutrality in the building sector. This study focuses on the dual temperature demand of space heating and domestic hot water in office buildings. A stratified thermal storage heat pump system is proposed, employing a zeotropic mixture (CO2/R1234yf) and industrial wastewater as a representative low-temperature heat source, as shown in Fig. 1. A typical office unit in Nanjing is selected for simulation, with annual thermal loads modeled using DeST-C software. A load-shifting operation strategy, nighttime heat storage, and daytime stratified supply are implemented. Furthermore, a Particle Swarm Optimization (PSO) algorithm is applied to optimize the control logic for heat pump operation dynamically. The results show that the temperature glide of the zeotropic mixture significantly enhances the temperature matching degree during evaporation and condensation processes. Under high-temperature output conditions (≥60 °C), the system achieves a seasonal average COP above 6.7 and reduces compressor energy consumption by 15%. This work offers both theoretical insights and practical guidance for the cascaded utilization of low-grade waste heat in urban buildings, supporting scalable and sustainable district energy applications.