Abstract: D-D (Double-Double) composite laminates greatly simplify the design and manufacturing of aerospace structures. In this work, continuously variable-angle fiber layup was introduced into D-D laminates to form a variable stiffness D-D composite laminate, followed by vibration analysis and fiber path optimization of the variable stiffness D-D laminate. Based on the classical laminated panel theory, a discrete solving scheme for the vibration control equation of variable stiffness composite laminates was derived using the generalized differential quadrature (GDQ) method. By combining the linear variation function of the fiber path with the optimization strategy of the direct search simulated annealing algorithm, efficient solutions for the vibration problem of variable stiffness D-D laminates and rapid optimization of fiber path were achieved. Calculations show that under CSCS boundary conditions, the first-order natural frequency of variable stiffness D-D laminated square plates rises linearly with the increase in ply counts. The variable stiffness layup scheme with large initial angles has a frequency that is over 10.86% higher than that of traditional Quad laminated plates. Compared to the Quad laminate, the optimization frequencies of the linear/curved mixed layer structure and the full curve fiber layer structure are increased by 35.68% and 44.78%, respectively. These findings indicate that introducing variable stiffness layers into D-D laminates can further improve frequency performance. This research verifies the effectiveness of the optimization process for variable stiffness D-D laminates based on GDQ, providing methodological support for efficient design of D-D composite laminates.