Abstract: To address the challenges in identifying energy transmission paths and optimizing structural responses of flexible structures under complex loads, this paper integrates power density flow theory with flexible multibody dynamic model to build an analysis and optimization framework. The Absolute Nodal Coordinate Formulation (ANCF), featuring geometric nonlinearity and continuous velocity fields, is employed to accurately capture local stress and velocity distributions and to enable visualization and optimization of power density flow. By combining the Green–Lagrange strain tensor with the elastic matrix, the theoretical expression for the vibration power density flow in a thin plate structure is derived, clarifying how stress and vibration velocity influence the energy propagation path and distribution. Using the power density flow analysis method, energy flow simulations are conducted for a satellite panel structure and a flexible double-link mechanism. A significant energy concentration is observed near connection points and hinge supports. Taking the energy density distribution as the optimization objective and keeping the total mass constant, the element thickness distribution is adjusted to mitigate the energy concentration effect. The optimization results show that the peak energy density of the flexible two-link mechanism is reduced by 68.5%, and the peak displacement response at the key position decreases by approximately 36%. For the satellite panel, the maximum energy density is reduced by 7%, and the peak displacement response at key positions decreases by about 12%, indicating a significant reduction in vibration levels. The proposed structural optimization method based on power density flow provides a new energy-based strategy for vibration suppression of thin-walled structures such as spacecraft, effectively overcoming the limitations of traditional modal analysis and offering important application value in structural dynamics design under complex load environments.