A novel high step-up DC-DC converter for distributed generation (DG) system is proposed in this paper. The concept is composed of three capacitors, three diodes, one inputinductor and one coupled-inductor. By utilizing the leakage inductor energy to charge capacitor, and convert energy by the coupled-inductor, high step-up voltage gain and high efficiency can be achieved with an appropriate duty ratio. The voltage stresses on the main switch and output diode are reduced by a passive clamp circuit. Therefore, low resistance R DS(ON) for the main switch can be adopted to reduce conduction loss. In addition, the reverse-recovery problem of the diode is alleviated, and thus, the efficiency can be further improved. The operating principle and steady-state analysis of the voltage gain are also discussed in detail. Finally, a 24-V input voltage, 400-V output voltage, and 200-W output power prototype circuit of the proposed converter is implemented in the laboratory to verify the performance.