This paper presents an isolated high step-up forward/flyback active-clamp converter with output voltage lift. In order to obtain high step-up voltage gain, the output voltage lift is adopted. The characteristics of the output voltage lift are similar to the forward converter in the charging mode and the flyback converter in the discharging mode. The active-clamp circuit is employed to recycle the leakage-inductance energy of the forward/flyback transformer and to suppress the voltage stress on the switch. By utilizing the active-clamp circuit, both primary and auxiliary switches can achieve zero-voltage-switching (ZVS), thus improving the efficiency of the proposed converter. Finally, a prototype circuit with 24-V input voltage, 200-V output voltage, and 400-W output power is implemented to verify the performance.