Abstract: To address the fracture failure of ball screw in brake-by-wire systems, a comprehensive investigation was conducted by using chemical composition analysis, hardness testing, metallographic analysis, macro/microscopic fractography analysis, mechanical property testing, and stress simulation analysis. The fracture was ultimately attributed to two synergistic factors: insufficient core toughness due to improper through-hardening heat treatment of the screw, and structural stress concentration in the screw design. These combined effects resulted in brittle fracture of the screw. Corresponding improvement measures, including optimized heat treatment processes and structural design modifications, were proposed and validated through rigorous testing.