With the intensification of the global energy crisis, building energy efficiency has become a critical issue for sustainable development. As China’s political, economic, and cultural hub, the Beijing area faces particularly prominent energy consumption challenges in its office buildings. Mixed-mode operated office buildings, which integrate air conditioning systems with natural ventilation, demonstrate significant potential for balancing energy conservation and occupant comfort. This study focuses on multi-story mixed-mode office buildings in the Beijing area, employing sensitivity analysis to systematically evaluate the effectiveness of passive technologies. First, a multi-story office building model was established to analyze the impact of various passive technology parameters—including orientation, building morphology, wall insulation, window-to-wall ratio, and natural ventilation—on energy consumption and indoor thermal environments. EnergyPlus software was then utilized for energy simulation to validate the model’s reliability. Based on simulation results, sensitivity analysis was conducted to propose optimized passive design strategies tailored to multi-story mixed-mode office buildings in Beijing. These strategies provide scientific guidance for architectural design and energy retrofitting, aiming to achieve a win-win scenario for building energy efficiency and indoor thermal comfort.