Bandwidth and tunability enhancement of difference frequency generation (DFG)-based wavelength conversion by introducing various distributing formats of p-phase shifting domains into the quasi-phase-matching (QPM) gratings is demonstrated, and the concise expressions describing the tuning curves in these cases are obtained for the first time. The results show not only the pump and signal bandwidth can be obviously broadened and flattened, but also diverse comblike pump-wavelength tuning curves with controllable channel spacing can be achieved by introducing periodically distributed p-phase shifting domains into the QPM gratings, which would greatly improve the tunability and practibility of DFG-based wavelength converters.