Steering knuckle is a key part in front axle of heavy truck, and its quality directly affects the reliability and safety of the whole truck. A kind of rupture in the steering knuckle resulting from forging and quenching tempering treatment was analyzed in detail. Through the analysis on the microstructure of specimens and rupture, it is found that the microstructure distribution of both surface and core part in sample is quite uniform, and both sides of the rupture have phenomenon of decarburization and oxidation. Combining theoretical analysis with other process factors such as heating temperature, die quality, etc.,the rupture was determined to form in the forging process and related to the surface quality of the blank. According to the analysis results, corresponding measurements were put forward as follows：the forging blank should reach the requirement of hot upset forging, and the nondestructive inspection was added to avoid the rupture in the forging process. The actual subsequent production verification shows that the analysis resulting in the steering knuckle rupture is confirmed and the effectiveness of the optimized measurement is proved.