Bolt breaking is one of engineering problems of deep roadway support. The form and mechanism of bolt breaking was studied by using site investigation and theoretical analysis. Following results were obtained: 1) The forms of bolt breaking in deep roadway are shear failure, brittle fracture failure, breaking failure, tensile failure, ejection failure and loosening failure; 2) Material defect and bearing behavior are the intrinsic cause of bolt breaking in deep roadway, and the extrinsic cause lies in the overload, namely the load of bolt exceed its limit load; 3) Under the combined effect of tensile load, shear load and torsion load, the effective diameter of the bolt decrease and the tensile stress in the bolt increase, as a result, the bolt is broken easily; 4) Coordinated control of bolt breaking and surrounding rock deformation in deep roadway can be realized using constant resistance and large deformation anchor bolt or secondary support technology. The results provide a reference for surrounding rock control of deep roadway.