通过宏观检验、化学成分分析、力学性能试验、金相检验及能谱分析等方法对10.9级高强螺栓断裂原因进行了分析。结果表明：在螺栓镦头成型工序中，头部R角部位产生折叠微裂纹，形成了早期裂纹源；在服役过程中，螺栓长期受交变工作应力作用，使得微裂纹进一步扩展，最终导致高周疲劳断裂。最后提出了相应的预防措施。

By means of macroscopic inspection, chemical composition analysis, mechanical property test, metallographic examination, energy spectrum analysis and so on, the fracture causes of 10.9 high strength bolt head were analyzed. The results show that in the forming process of bolt head,folding micro cracks formed on the R angle area of head,which became the early crack source. During working time, the bolt head subjected to alternating work stress for a long time, thereby furthering the expansion of micro cracks, and eventually caused the high cycle fatigue fracture. Finally, the relevant preventive measures were put forward.