In 2009, the interesting photochromic complex o-MeCN and its isomeric close form c-MeCN were synthesized and investigated, which would transform to each other according to the characterization of UV and visible irradiation. In our work, the excellent nonlinear optical (NLO) properties are obtained by theoretical calculating. Results show that the β_tot value of c-MeCN is about 12 times as large as that of o-MeCN in acetonitrile solvent, which provide a basis for NLO switch. Further, the UV–visible absorption spectrum can confirm that the remarkable β_tot values for c-MeCN are mainly attributed to the charge transfer induced by the photocyclization. Significantly, the β_tot values reduced with the increasing of dielectric constant ε of the solvent, and the differences of β_tot values between the open and close form, present a regularly change in different solvents. This reversible photochromic process and solvent effect may open up new opportunities for the discovery of attractive NLO switch.