All-optical wavelength conversion based on four-wave mixing (FWM) is one of the key technologies in future multi-wavelength telecommunication systems. Besides semiconductor optical amplifiers, semiconductor lasers are also good candidates for wavelength conversion. The influences of the residual F-P cavity mode on the non-degenerated FWM in a distributed-feedback (DFB) laser have been investigated from small to large range frequency detuning, as well as the conversion efficiency of conersion FWM. The experimental results show that the conversion efficiency of FWM can be enhanced obviously by the cavity resonance when the probe wavelength matches the F-P cavity mode; the FWM with high conversion efficiency can be achieved when the frequency detuning between the injection probe frequency and free-running frequency of DFB laser is up to terahertz.