Abstract: The sectional-area distribution significantly influences the hydraulic performance of hydrodynamic turbo-machinery, particularly the torque converters. Conventional torque converter designs often adopt an equal-sectional-area-distribution approach to minimize hydraulic losses, neglecting the full potential of sectional-area distribution parameters for performance optimization. To address this, a novel modeling method and a corresponding torus design approach were proposed to accurately describe and utilize sectional-area distribution in this paper. Firstly, a comprehensive cascade design system was developed based on variable sectional-area distribution for torque converters to complete the examinations in-depth of their unique characteristics and performance implications. Then, a design of experiments (DOE) method was used and multiple cases with different sectional-area distributions were designed and evaluated to assess the influence of sectional-area distributions on hydrodynamic performance. And then, exploring optimal sectional-area distribution designs of various impellers, an integrated optimization design result was achieved for the enhanced optimized torus design. Finally, the substantial improvements were demonstrated by experimental results, achieving a remarkable 18.5% increase in pump torque and a significant 3.9% enhancement in torque ratio. The results affirm the effectiveness of the proposed approach in enhancing torque converter performance without altering overall dimensions, highlighting the importance of considering variable sectional-area distribution in torque converter design.