Abstract: Cracks were found in a batch of valve spool units of lead brass during processing. The reason of cracking was analyzed by means of chemical composition analysis, hardness testing, macroscopic and microscopic examination, X-ray diffraction, following with several suggestions for improvement. The results showed that brittle fracture under local stress had led to unit failure. And it was mainly caused by excessive lead and impurity elements content, as well as insufficient annealing.