Automotive B-pillar is an important part of the body structure, and the B-pillar of TC4 titanium alloy sedan is taken as the research object to analyze the difference of mechanical properties related to titanium alloy B-pillar and traditional material Q235 B-pillar. ANSYS software is used to carry out static analysis and modal analysis under certain constraints on the B-pillar of the two materials to evaluate the influence of different materials on the mechanical properties of the B-pillar. Then the titanium alloy B-pillar was optimized by topology optimization and adding reinforcing rib. The results show that: Compared with the Q235 B-pillar, the deformation and natural frequency of the TC4 titanium alloy B-pillar are not much different, which meets the design requirements, and the mass is reduced from 16.601 kg to 9.184 kg, which is 43%. After optimization, the static properties and natural frequency of the TC4 titanium alloy B-pillar are improved compared with those before optimization, and the mass is reduced to 7.622 kg again.