A digital-phase-locked-loop (DPLL)-based backlight module is proposed to reduce the leakage current effect in liquid crystal display (LCD). In this paper, the mathematical model of the cold cathode fluorescent lamp (CCFL) current, including the parasitic capacitance in LCD panel, is conducted to explore the influence of leakage current effect. Moreover, the primary-side control and the DPLL function are integrated to form a feedback mechanism to track the optimal operating frequency. Then, the influence of parasitic capacitance can be reduced so as to eliminate the leakage current effect. The experimental results agree with the theoretical predictions.