In order to determine the influencing factors of geological environment at underground tunnel, we carry out specific investigation by using methods such as in-situ interview and indoor statistical analysis. Engineering geological environment at 28 typical tunnels in Chongqing is taken as example. Results show that geological environment at underground tunnel is influenced by hydrogeological condition, lithology, waterproofing measure, construction method, geological structure, buried depth of tunnel and so on. In particular, hydrogeological condition is the controlling factor and lithology is the main factor. Meanwhile, we give suggestions to protect underground geological environment, which offer reference for administrators to specify the protection techniques of underground geological environment in Chongqing.