Abstract: Boundary surface analysis method for workspace of double-octahedron variable geometry truss robotic manipulators(VGTRM) is proposed in this paper. Based on surface analysis and analytical method of direct displacement analysis, the analytical surface equations of double-octahedron VGTRM are derived. Precise shape of double-octahedron VGTRM(s workspace boundary surface is drawn. Analysis and calculations show that the workspace of double-octahedron VGTRM is enveloped by six surface patchs.