The invention belongs to the technical field of organic optoelectronic materials, in particular to a transition metal complex as a phosphorescent material as well as a preparation method and application thereof. The transition metal complex is characterized in that emitted light wavelength of a material can be adjusted within a wider wavelength range by matching Z1, Z2 and Z3; meanwhile, a main ligand further finely adjusts the wavelength of emitted light by heteroatoms, which has important value for obtaining luminous materials with various wavelengths. The complex prepared by the preparationmethod disclosed by the invention has high luminous efficiency; in addition, the wavelength of the emitted light can be adjusted within a wide range. The main ligands of the complexes have the same skeleton structure; the adjustment of the emitted light wavelength within the dark red light range is realized by changing the positions of functional groups, the positions of the heteroatoms on the main ligands and the species of the heteroatoms. Besides, preparation methods of the luminous materials with different colors are basically identical and are simple in operation.