Abstract: Two M27 double-head bolts fractured during the installation. The causes of bolt fracture were analyzed by means of macroscopic observation, chemical composition analysis, mechanical property test, scanning electron microscope and energy spectrum analysis, metallographic examination. The results show that there were hydrogen embrittlement cracks in the double-headed bolts before the galvanizing process, which led to one-time fracture under the action of external force when the bolts vere installed. The high hardness and strength of the double-headed bolt led to the increase of the hydrogen embrittlement sensitivity of the material, which further increased the risk of hydrogen embrittlement cracking.