In this paper, a comprehensive broad_band dynamic model of tunable wavelength converter based on four_wave mixing in semiconductor fiber ring laser is presented. Critical factors, e.g., the materal gain profile, the longitudinal variation of the optical field, and the broad_band spontaneous noise emission are considered in the model. By numerical simulation, the effects of the input signal power, injection current, the coupling of the output coupler and the lasing wavelength on the performance of the wavelength converter are investigated. Numerical results are in agreement with the experimental results in the literature