In the context of urban renewal, how to meet the public’s demand for spatial quality in existing underground commercial streets has become an urgent problem to be solved. Corner space, as an important node in the pedestrian system of underground commercial streets, is a key area that affects spatial vitality, walking direction, pedestrian physiology, and psychology. Based on a pedestrian-friendly perspective, the impact of distance, constituent elements, and angles between different underground corners on pedestrian behavior is explored, and an adaptive corner space optimization strategy for (single building) underground commercial streets is proposed using spatial operation methods. The study aims to provide practical application value for optimizing the design of corner spaces in underground commercial streets. The results indicate that: Using obtuse corner angles, appropriate corner spacing, and increasing the boundary area at the corner can effectively enhance the overall vitality of the street and the attractiveness of shops.