Abstract: A large 9Cr2Mo steel cold rolling roll broke while waiting for tempering after quenching. The fracture cause of the cold rolling roll was analyzed using macroscopic observation, chemical composition analysis, metallographic examination, mechanical property testing, scanning electron microscopy and energy spectrum analysis. The results show that the hydrogen content in the large cold rolling roll of 9Cr2Mo steel was high, and the quenching stress was high, and resulted in hydrogen embrittlement fracture of the cold rolling roll. The presence of more inclusions and severe dendrite segregation provided a place for the accumulation of hydrogen elements, promoted the fracture of the cold rolling roll.