This paper investigates the application of a planar deployable structure with screw theory and discusses its possible applications in overconstrained lift platforms via calculating its stiffness. These platforms are all made up of a number of identical scissor-form pivoted links. Compared with their traditional counterparts, the lift platforms with planar deployable structures have higher stiffness and higher strength in applications because every lift platform is multiplane overconstrained mechanism connected by a strengthened frame at each deployable layer. In operation, these deployable structures are always symmetric about the vertical central axis connecting the moving platform and the fixed one. Therefore, the stress conditions of the links in each layer can be assumed to be identical as the lift platform is moving up and down. Prototype test illustrates the innovation of the lift mechanisms while keeping the same load capacity.