Abstract：The cold bending cracking samples of Q235B H-beam steel were analyzed by macroscopic examination， chemical composition analysis， mechanical property test and metallographic examination. The results showed that in the process of cold bending test， the bonding property between thick strip plastic inclusions and point chain brittle inclusions was poor. Due to inclusion shedding or peripheral stress concentration in cold bending test， the gaps or micro cracks were formed. With the strengthening of stress， the cracks were extended to form the source of cold bending crack. The banded structure and machining marks in the process of cracking accelerated the expansion of cracks.