Abstract: The reason for cold bending cracking of Q345D steel plate was analyzed by macroscopic observation, chemical composition analysis, mechanical property tests, fracture analysis, gold phase test and hardness test. The results showed that chemical composition, matrix tissue, and mechanical properties of steel plate met technical requirements. During cutting, groove was formed on the side of steel plate, and groove was martensitic structure, the plasticity was poor, stress concentration was generated at this position during bending process, which was the root cause of cold bending cracking of Q345D steel plate.