Abstract: A certain die cast aluminum alloy steering knuckle broke. The reasons for the fracture of the steering knuckle were analyzed using macroscopic observation, chemical composition analysis, industrial computer tomography imaging analysis, scanning electron microscopy and energy spectrum analysis, metallographic examination, mechanical property testing. The results show that the fracture of the steering knuckle mainly concentrated in the upper surface near the outer diameter area, and there were casting defects such as looseness and cracks near the fracture. Stress concentration occurred at the defect site, causing a decrease in the strength of the material. Under the action of the pressing force, cracks appeared at the defect site, and the cracks continued to propagate, ultimately leading to ductile fracture of the steering knuckle.