The results showed that there existed original defects in the pin shaft surface,and the pin shaft bore bend and shear load which wear of chain plates during long-term service enlaryed the dearomce of the plates,original defects and wear of chain plates caused the chain pin shaft fatigure failure.

Accurate analysis of the contact stress between components of the pin connection and study concerning the effect induced by various parameters on the magnitude and distribution of contact stress are very important to better design and application of pinned connections.

Through analysising,geted the main reason of creating crack is a loose layer existing at the outside side of the conjunction slice of the chain,and there are many defects at outside of the link bore.