The invention provides a satellite platform structure with a downward-stretching storage box. The satellite platform structure comprises a conical force-bearing cylinder, a downward-stretching storagebox mounting structure and an instrument and equipment mounting structure. A main force-bearing structure adopts the conical force-bearing cylinder, thus, force transferring is direct, and the weightis smaller; through a storage box mounting mode provided by the storage box mounting structure, the storage box stretches downwards to a rocket three-dimensional frustum area so as to lower the masscenter of a satellite; and the outer configuration of the instrument mounting structure is in a non-equilateral hexagon shape so that a larger equipment mounting space can be provided, and adaptive design is conducted on one side of the hexagon so as to provide an antenna mounting space. Compared with the prior art, the satellite platform structure with the downward-stretching storage box has thefollowing advantages that firstly, the storage box is mounted in a downward-stretching mode, so that the mass center of the satellite is lowered greatly; secondly, bearing of high-capacity propellantsand response control can be provided through the design of pull rods and an embedded frame in the storage box mounting structure; and thirdly, through the non-equilateral hexagon outline, the wider equipment mounting space can be provided, the force transferring path is direct, the structure is simple, the weight is small, and the satellite platform structure is suitable for a deep space probe and can be popularized to the configuration design of medium and large satellites.