Abstract: Taking the forging process of brass valves with Haff hot forging dies as the research object, this paper conducts a systematic study on three types of hidden defects, namely surface peeling, interlayer folding, and cracking, which occur frequently and are seriously harmful in production. Through analyzing the microscopic mechanisms and influencing factors of defect formation, combined with actual production cases, the results show that billet dimension parameters, die structure design, heating process, and lubrication conditions are the core factors leading to defects. Based on this, targeted preventive measures such as billet gradient heating, optimization of die exhaust system, reasonable control of height-diameter ratio, and selection of graphite-type release agent are proposed. Practical application shows that these measures can increase the comprehensive qualification rate of brass hot forgings by more than 12% and significantly reduce production costs. The research results provide practical technical references for the optimization of brass hot forging process and die design.