Stress - balanced state of tunnel surrounding rock will be destroyed, during tunnel excavation under adverse geological conditions, which will result in the occurrence of tunnel large deformation and other adverse events. For further study of grouting anchor supporting mechanism, analysis and calculation of plastic deformation zone and surrounding rock potential fracture surface had been done. Key parameter calculation formula of bolt arrangement and effective length was derived. Theoretical research results were verified by a case of anchor reinforcement in circular tunnel. The conclusions had been drawn that: (1)Tensile stress of surrounding rock will transfer to the surrounding through grouting anchor, improving the compressive strength and elastic modulus. (2)Earth pressure and radial deformation can be reduced by increasing of compressive strength and elastic modulus. (3)Reinforcement effect of grouting anchor will be affected by various factors, such as material, length, diameter, tensile strength, and so on.