A novel high step-up DC-DC converter for fuel cell (FC) system is proposed in this paper. By utilizing the coupledinductor, energy can be transfer to secondary side and charge step-up capacitor at the duration of magnetizing inductor are charged by input voltage. Part of leakage inductor energy charge clamp capacitor and convert to step-up capacitor. High step-up voltage gain and high efficiency can be achieved by input voltage, step-up capacitor and the secondary side output with an appropriate duty ratio. By using active clamp technique, voltage spike of main switch can be reduced and the leakage inductance energy can be recycled. However, the leakage inductor induces large voltage spike on main switch when it turns off. The voltage spike on the main switch are reduced by an active clamp circuit. Therefore, low switch-turn-on resistance RDS(ON) for the main switch can reduce conduction loss. In addition, high switching frequency designed reduces the physical volume. The operating principle and steady-state analyses of Continuous Conduction Mode (CCM) of the voltage gain are also discussed in detail. Finally, experimental results taken from a 200-W prototype circuit with a 24-V input voltage and 400-V output voltage are reported to verify the performance of the proposed converter.