A numerical and experimental analysis of an erbium-doped linear cavity laser is presented. In particular a numerical model for the laser continuous wave and multiwavelength operation has been developed. In the proposed approach, according to the spectral model, the propagation rate equations have been used to predict the evolution of forward and backward signals and amplified spontaneous emission in the doped waveguide and properly boundary conditions have been imposed to describe the resonant etalon. The performances of the erbium-doped linear cavity laser are investigated in detail and the best parameters to optimize the laser design as, for example, the mirror or grating reflectivities, the cavity length and the pump power are investigated. Comparisons with experimental data confirm the validity of the approach. Numerical results point out the model usefulness for device design.