Abstract: Crack happened at the brass valve after hot forging. The cracking causes of the hot forged brass valve were analyzed by chemical composition analysis, metallographic examination, scanning electron microscopy and energy spectrum analysis. The results show that the hot brittleness was the main reason for cracking of brass valve. During hot forging process, segregation of lead occurred along the grain boundary and formed low melting point eutectic phase with high lead, which caused weakness of the grain boundary. Cracks originated from the surface of the valve body and propagated along the axis under the tensile stresses and resulted in the brittle cracking. Finally, preventive measures were put forward for the cracking causes of the brass valve.