The design method of 3-element centripetal-turbine hydrodynamic torque converters was investigated. A new design method based on torus streamline was proposed. The particle movement inside the hydrodynamic torque converter was considered as the curvilinear movement on a torus surface, and could be decomposed into meridional component movement and circumferential component movement. The meridional streamline equations and torus streamline equations were derived. The blade influence on streamline was analyzed and a streamlined thickness function was put forward. The equations of blade camber line combined with the thickness function, the blade surface equation was obtained. The research result shows that either a meridional streamline or a torus streamline is an approximate parabola. 