The invention relates to a float unit and a combined water platform. The float unit comprises a float body, a bearing body and a ballasting device; the ballasting device comprises a balancing weight and a water inlet-drain device; the water inlet-drain device comprises a pump and a float unit water inlet-drain connector, the float unit is subsided or lifted by injecting or ejecting an approximate amount of water; when the float body suspends underwater, at least one part of the bearing body exposes and is kept on the water; the float unit is provided with a generating device, the water platform formed by the float unit is formed by the connection of a plurality of float units. The float unit is lower in manufacturing cost, high in intensity, and convenient to install and construct in a large area; the float body suspends below the sea surface and can be slightly affected by stormy waves, and a wavy generating device can restrain the rocking function of sea waves, and has a capacity of resisting against severe sea conditions. According to the float unit and the combined water platform provided by the invention, the marine energy in large area can be acquired, the generating cost can be reduced, and the comprehensive generating efficiency can be improved, therefore a feasible solution can be provided for the development and use of ocean energy resources in a large-scale and commercial way.