Objective To investigate the mechanisms by which single- and double-volute structures, along with different expansion cone angles, regulate the internal flow characteristics and haemolysis performance of centrifugal blood pumps, thereby providing a theoretical basis for the synergistic optimisation of blood pump volute structures. Methods Based on a circular cross-section as the fundamental configuration, single-volute (s) and double-volute (d) structures were designed. Gradual cone angles of 30°, 45° and 60° were set to regulate the rate of change in the flow channel cross-sectional area, and RANS steady-state numerical simulations were performed using ANSYS 2024 R2. Results The head of both single- and double-volute configurations exhibited a decreasing trend with increasing cone angle; at the same cone angle, the head of the single-volute configuration was consistently higher than that of the double-volute configuration; The hemolysis index follows the pattern s60 < d45 < d30 < s30 < s45 < d60; the single-volute design at 60° exhibits the lowest hemolysis index (7.43×10??) but the greatest head loss; At 45°, the double-volute design exhibits the smallest high-turbulence kinetic energy zone, with the high-turbulence kinetic energy zone in the diffusion tube disappearing entirely; the scalar shear stress distribution is more rational, achieving an optimal balance between head (98.69 mmHg) and haemolysis index (9.39 × 10??); The symmetrical structure of the double-volute design optimises flow field uniformity and reduces energy dissipation; however, the large 60° cone angle exacerbates flow separation due to excessive diffusion, thereby offsetting the structural advantages. The research findings provide theoretical guidance for the cross-sectional design of centrifugal blood pumps.