This invention is directed to a column floater with extended cylinder and a ring buoy-group, which comprises an upright buoy at a water surface, an extended cylinder, a positioning system and a topsides. The top of the upright buoy is above the water surface and a moonpool is either set or not in the center of the upright buoy through the top to the bottom. The extended cylinder, connecting to the bottom of the upright buoy and extending downwards, includes two types of fixed and sliding to form a column floater with fixed extended cylinder and a column floater with sliding extended cylinder respectively. The positioning system is one or two combined of mooring system and DP system. The column floater with extended cylinder is a new type floating platform with multi-purpose, combining advantages of the spar platform and the current cylindrical FPSO, high performance, safety and reliability.