Abstract: This article focuses on the increasing development scale of underground spaces in China in recent years, which have gradually developed from a single function to a multi?functional composite space. Based on the technical perspective of building fire protection design, this article analyzes the construction characteristics and fire risk characteristics of multi?functional composite underground spaces, and analyzes the problems of multiple fire risk factors, difficult evacuation and rescue, and heavy fire consequences in underground spaces. Taking the underground space of Beijing CBD as an example, this article establishes a research method of modular block analysis and difficult point argumentation, explores and optimizes the technical points and strategies of multi?functional composite underground space fire protection design, and provides reference for urban multi?functional composite underground space fire protection design, construction, and inspection management.

Key words: multi?functional composite underground space, fire risk； fire protection design