Abstract: For enhancing the operating range of vehicle mounted E-O system and keeping better observing ability when the vehicle is concealable, an elevator mast system which could burden a long-range E-O system was designed. The compound transmission mode which combines the hydrolic drive with the mechanical transmission assembly is adopted. The square structure is used by the mast, whose length-width ratio is controlled within 1∶20. It is made of aluminium alloy, and its well thickness is more than 3mm. Its raising height is 10m, the duration of rising up or getting down is 1min, and the maximum loading capacity is 200kg. The loading capability, wind resistance and vibration characteristic of the mast are analyzed. A spring take-up without slip ring is presented, which is suitable for the signals to go to or come from the mast and the current to reach to the optical systems mounted on the top of the mast.