The C-type expansion bolt is a new kind and new structural bolt. It has superior compatibility to the soft rock and the big distorted tunnel. In order to study its stress, deformation and interaction mechanism, large distortion calculations and analyses have been carried out on the bolt by FEM (finite element method), especially with the ANSYS software, based on the updated Lagrangian law. The results show that the maximum stress and deformation of the section and body of the bolt meets the anchoring requirements. The bolt meets the required anchoring performance and anti-drawing performance. The paper provides some basis for its design, application and anchoring stress analysis.