Abstract: Cracking occurred on the edge surface of a Q355B steel. The cause of crack formation was analyzed using methods such as macroscopic observation, chemical composition analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that surface cracks on the steel plate occurred during the continuous casting process, and there was an accumulation of harmful elements such as arsenic and copper near the cracks. Harmful elements such as arsenic and copper formed low melting point enriched phases, which deteriorated the plasticity of the steel plate and disrupted the continuity of the steel matrix. Under the action of tensile stress, the surface of the steel plate cracked.