Abstract: In view of the problem of batch of unqualified low temperature impact absorbed energy of Q345E steel plates with thickness of 70 mm, means such as macro analysis, chemical compositions analysis, metallographic examination, scanning electron microscopy analysis were used to find out the unqualified reasons, combined with production process investigation. The results show that coarse matrix microstructure and existence of a lot Widmanstatten and inclusions of MnS and strip oxide in the steel plates were the main causes for the unqualified low temperature impact absorbed energy. On this basis, rectification measures were put forward, and recurring failure phenomenon was avoided effectively.