A novel tridentate ligand (L), N-(4-methylbenzyl)-N′-(2-(4-methylbenzylamino)ethyl) ethane-1,2-diamine and its transition metal complexes [ML(H2O)2Cl]Cl (M=CuⅡ, CoⅡ, NiⅡ) have been synthesized. Their composition and structures were characterized by elemental analysis,1H NMR, FT-IR and molar conductance. The crystal structure of the Ni-L was determined by single crystal X-ray diffraction method. L is a tridentate ligand, which coordinate to Ni atom with 1:1, and all of the complexes have similar six–coordinated octahedral structures. In addition, the interaction of the complexes with calf thymus DNA was investigated by UV spectroscopy and fluorescence spectroscopy, and the results suggested that the complexes may bind to DNA by electrostatic interaction mode. The binding constants (Cu-L, Ni-L, Co-L) are 2.99×104, 9.78×103 and 3.66×103, respectively.