in this research we have studied the effect of some transition-metals (cu, ag and au) substitutions on two-electron reduction potential of flavins by application of dft method. all geometries have been optimized at blyp level of theory and “6-31+g** + lanl2dz” mixed basis set. the frequency job at the same method and basis sets has been performed to obtain gibbs free energy of compounds. it has been shown that substitution of these three metals on flavin decreases the reduction potential of flavin. the trend is ecu< eag < eau< eunsub. therefore, these transition metals can be considered as electron donor group. by substituting these metals together with other functional groups such as –oh, -ch3, -cl, -cooh, -no2 in different positions of the ring we have obtained more wide range of potential values. the maximum decreasing percent in potential value is 46.80% for 7,9-cu-6,8-oh-f. also, we found a significant substituent effect on the planarity of the reduced flavins, if c6, c7, c8 and c9 binding with an electron-withdrawing substituent, the reduced flavins turned to be more planar, such as no2. however, electron-donating substituents make flavins more flexural.