The second-order nonlinear optical (NLO) properties of a series of dithienylethene- (DTE-) containing Pt(II) complexes have been investigated by density functional theory calculations. The first hyperpolarizabilities beta of studied systems can be greatly enhanced by simple ligand substitutions. Because of the nature of DTE units, the beta values also can be varied by the use of lights in the studied systems. The highest beta difference between photoisomers can over 1000 x 10(-30) esu, with the contrast around five times. Thus, the studied systems can act as effective photoswitchable second-order NLO materials. The time-dependent density functional theory calculations revealed that the charge transfer patterns of studied systems have special characters compared to other reported DTE-containing NLO switched chromogens, the DTE units mainly act as electron-donors in studied systems, and the variation of beta can be viewed as alternation of donor abilities of DTE units; thus, our work also proposed a new mechanism for designing photoswitched NLO multifunctional materials.