Abstract：The previous design methods of bolt in tunnel are based on empirical analogy and simple theoretical method. Because monitoring data and relative factors are not fully considered，the reasonality and safety of design by them are not assured in complex and variable circumstances and they cannot be applied in the cases without analogous examples. So based on the first case of strong extrusion tunnel in China，the determination of rock bolt parameters in strong extrusion tunnel is discussed. A method based on the logarithm spiral angle is put forward in this article. And its application is discussed in detail. It is presented that the zone where the bolts are affected by surrounding rocks can be divided in two zones，the vertical tension zone and the strong extrusion shear zone or the horizontal tension zone. And the load with which surrounding rock acts on bolts is also given. Based on the case of Jiazhuqing tunnel，the process of the method is illustrated and the method is proved.
