To obtain high stiffness and lightweight truss structures, a space truss structure optimization design method based on the branching growth mechanism of plants was proposed. By simulating the growth, branching, and degeneration processes of plants in natural environments, the space truss structure can adaptively grow based on load and boundary conditions, directly obtaining information on truss distribution and profile dimensions. Design discussions were conducted on the typical space truss structure, including simply supported beam-type truss, cantilever beam-type truss, and L-shaped truss under bending and torsion conditions. The results demonstrate that the design method converges quickly to the optimal structural layout, unaffected by the base structure's mesh density. Further design validation was carried out on a practical example of an escalator truss. The optimized escalator truss improved stiffness, reduced weight, and achieved the design goal of high stiffness and lightweight, indicating the method's strong potential for engineering applications.