Abstract: To study the CrCr bonding in linear trichromium complexes Cr3(dpa)4Cl2, the structures of symmetrical conformation 1, unsymmetrical conformation 2 and their oxidized species Cr3(dpa)4Cl2+ 3 were investigated by density functional theory (DFT) and natural bond orbital analyses, and the following conclusions can be drawn. (1) In 1 and 2, there is only a 3-center-3-electron bond which is delocalized over the Cr36+ chain. The electron charge of dz2 orbitals transfers from terminal Cr atoms to central Cr atom with spin, while from central Cr atom to terminal Cr atoms with spin. The delocalization of electron is more remarkable. Ligated by a spiral set of dpa- ligands, the dxz and dyz orbitals of each Cr atom in two molecular orbitals turn around on metal chain (Z axis) in varying degrees and make it difficult to form bonds. (2) In 3, the spiral force from dpa- ligand also turns the dxy orbital of each Cr atom around on Z axis in varying degrees and makes it impossible to form bond in CrCr short bond. Therefore, there is only a triple bond in the short CrCr bond, which is different from a quartet CrCr bond reported by some literatures about theoretical analysis. (3) In 1 and 2, the HOMO is a nonbonding orbital concentrated mainly on terminal Cr atoms. The terminal Cr atoms act as the electron donor upon oxidization to 3.