Abstract: Otain the necessary and sufficient condition that the subsystem lattice of a completely regular semigroup S is a semimodular lattice, that is, the subsystem lattice of S is a semimodular lattice if and only if S is the order sum of some UM-groups or left [right] groups whose maximal subgroups are UM-groups.

Key words: completely regular semigroups, completely regular subsemigroups lattice, semimodular lattice