A PbSe quantum dot (QD) doped fiber laser of 1550 nm is simulated numerically by solving the rate equation and lasing propagation equation in a ring resonator, on the basis of experiment using the QDs hosted in ultraviolet (UV) gel as lasing medium. It is shown that the simulated results are consistent with the experiments observed before, including the pumping threshold, single/multi mode laser power varying with the pumping power, desirable doping concentrations, and single mode laser power varying with the outputting coupling ratio. The inversion condition of population density, N2/N1≥0.45, is given by investigating the laser power distributing along the longitudinal fiber, which can be explained by the cross-section ratio of absorption to emission at the 1550 nm. A rang of available doping concentration is determined by studying the effect of the doping concentration on the laser power.