Abstract: Fracture of hydrogen compressor cylinder head bolts happened in a petrochemical company, and the fracture reasons were analyzed by means of macro and micro fracture analysis, chemical compositions analysis, microstructure examination, and tensile and impact test. The results indicate that the fracture originated at the threaded end of connection of the screw head and bolt where the stress was concentration. Because the stress concentration, coupled with the low grade of bolt strength, the low stress high cycle fatigue fracture occurred for the cylinder head bolts under the long term coaction of reciprocating alternating stress and torsion stress.