Urban underground space, a vital natural and strategic resource for cities, includes dense geological bodies (rock, soilwater, gas), natural caves, and artificial facilities like goafs, basements, underground transport, and municipal networks.Its development forms an industrial chain covering geological survey, planning, construction, equipment manufacturingand operation management. This paper focuses on geological exploration at the chain's forefront, advocating "overallplanning-led, prior geological survey." It systematically defines key detection elements of geological surveys, establishinga targeted index system of geological factors. The system addresses differentiated needs across urban planning stages(preliminary, design, construction) and geological types (karst, soft soil, fractured rock). It specifies critical engineeringparameters (e.g., rock-soil mechanics, groundwater, geological structures) and environmental factors (e.g., seismic riskskarst intensity) for each scenario. The findings provide a structured framework for geological exploration in undergroundspace development, enhancing safety, scientific rigor, and sustainability in resource utilization.