The influence of geological factors on loose zone of surrounding rock is analyzed by taking an extralong deep tunnel in Chongqing for example. The formation, development and distribution of loose zone of surrounding rock of tunnel are studied by means of numerical simulation method, orthogonal test and field test. The results show that: 1) The internal friction angle and cohesion of the tunnel surrounding rock have a negative correlation with loose zone of surrounding rock. 2) The side pressure coefficient and buried depth have a positive correlation with loose zone of surrounding rock. 3) The internal friction angle and buried depth are the main factors of loose zone of surrounding rock. The distribution of loose zone of surrounding rock of tunnel under different geological conditions can be aware of; and then the tunnel support parameters can be optimized timely so as to guide the tunnel constrution with safety and efficiency according to the study results.