Based on a type of nested cw Raman fiber laser, the loss characteristics of the Raman fiber, fiber Bragg gratings, and splicing in the laser cavity are described. Their impacts on laser performance are analyzed through numerical modeling. The optimal cavity parameters are obtained and agree well with the predicted laser output in the experimental result. Meanwhile, the spectral broadening of the laser output and its influence on the simulation accuracy are discussed for the first time in nested Raman fiber lasers. With the improved modeling, more accurate simulations are realized.