In this paper, a simple yet efficient method is proposed to improve the performance of dye-sensitized solar cells (DSCs) by modification after sensitization using Mg(OOCCH3)(2), With modification of Mg(OOCCH3)(2), a blue shift of the absorption peak and optical hand gap were observed in the UV-vis spectrum. As shown in the Fourier transform infrared spectrum, the intermolecular hydrogen bonding of N3 dye, which caused the aggregation of dye molecules, was weakened. As shown in the I-V characteristic, the conversion efficiency of the DSCs was improved by the treatment of Mg(OOCCH3)(2). Furthermore, the charge recombination was retarded as evidenced by the decreased dark current and the slowed decay rate of the dye excited state, which were characterized by the I-V curve in dark and transient photovoltage spectra. The mechanism of this modification process was also proposed further. Modification with Mg(OOCCH3)(2) facilitated the electron injection from the dye molecule to the conductive band of TiO2 by raising the excited state energy level of the dye molecule. This energy level rising was evidenced by the results of the cyclic voltammetry test and the blue Shift Of the optical hand gap. Furthermore, Mg(OOCCH3)(2) worked as an insulating barrier layer at the sensitized TiO2/electrolyte interface, thereby retarding the charge recombination in DSCs.