In this paper, the design of Radio Frequency (RF) Micro Electro-Mechanical Systems (MEMS) phase shifter using step tapered Co-Planar Waveguide (CPW) are analyzed. The step tapered CPW are used as the transmission line instead of conventional CPW. The design consists of a CPW transmission line periodically loaded with MEMS switches. An analog control voltage applied to the center conductor of the CPW line and ground varies the phase velocity of the loaded line by pulling down the MEMS switches to increase the distributed capacitance. The change in phase velocity yields a phase shift in the Distributed MEMS Transmission Line (DMTL).