Efficient wavelength conversion using distributed Raman gain and the Raman-assisted parametric four-wave mixing in 1 km of highly nonlinear fibers (HNLFs) is demonstrated in this letter. We present the theoretical analysis of the Raman-assisted parametric process and investigate the mechanism of wavelength conversion between parametric Stokes and anti-Stokes light. The system is implemented in a double-pass Raman amplifier where a tunable optical bandpass filter and a wide-band reflector are used to form a laser oscillation in the normal dispersion region of HNLF. The lasing light acts as the parametric pump to enable the wide-band wavelength conversion about the pump wavelength. Conversion efficiency greater than 0 dB over 50 nm is obtained and the converted idler wavelength can be adjusted more than 10 nm continuously by tuning the tunable optical filter. Hence, an arbitrary new wavelength can be converted within the tunable range of optical filter with high efficiency.