Abstract: Multi-wavelength fiber lasers have important applications in the fields of dense wavelength division multiplexing (DWDM), nonlinear frequency conversion, optical fiber sensing and so on. At present, there are many different kinds of methods that can achieve multi-wavelength fiber laser output. Among them, nonlinear polarization rotation (NPR) is a commonly used method. In this paper, theoretical analysis about NPR fiber filter near 1550 nm is conducted. The simulations include the influence of output angle, fiber birefringence and length of single-mode fiber on optical spectrum filtering effect; the relation between free spectrum range (FSR) and laser central wavelength; the relation between FSR and optical path difference in orthogonal directions. Through systematical simulation about the optical spectrum filtering effect of NPR fiber filter, the effects of different parameters on the optical spectrum filtering are analyzed, which are beneficial to the experimental study about multi-wavelength fiber lasers.