  Charge density wave (CDW) in kagome materials with the geometric frustration
is able to carry unconventional characteristics. Recently, a CDW has been
observed below the antiferromagnetic order in kagome FeGe, in which magnetism
and CDW are intertwined to form an emergent quantum ground state. However, the
CDW is only short-ranged and the structural modulation originating from it has
yet to be determined experimentally. Here we realize a long-range CDW order by
post-annealing process, and resolve the structure model through single crystal
x-ray diffraction. Occupational disorder of Ge resulting from short-range CDW
correlations above $T_\mathrm{CDW}$ is identified from structure refinements.
The partial dimerization of Ge along the $c$ axis is unveiled to be the
dominant distortion for the CDW. Occupational disorder of Ge is also proved to
exist in the CDW phase due to the random selection of partially dimerized Ge
sites. Our work provides useful insights for understanding the unconventional
nature of the CDW in FeGe.
