Tapered fiber has unique advantages in suppressing nonlinear effects because its core radius increases uniformly along the length of the fiber. In this paper, the output spectrum evolution and Raman performance of three different types of passive fibers are simulated and analyzed under the input of single transverse mode Gaussian beam: the passive fibers with constant core radius, linearly increasing radius and nonlinearly increasing core radius, all have the same input core diameter of 50 μm. Under the same conditions, when the input power is 10 kW, the Raman suppression ratio (defined as the difference between the intensity of the signal peak and the Raman peak in the spectrum) of constant type passive fiber is 33.1 dB, while those of the linear type and nonlinear type are 47.0 dB and 48.6 dB, respectively, which are better than that of constant type by 13.9 dB and 15.5 dB; When the input power reaches 17.5 kW, 81.6% of the input energy of the constant type is dissipated or transferred to other wavelengths, while that of linear and nonlinear types is less than 2%, and the output signal optical band energy accounts for 98.1% and 98.9% of the total input energy. The results show that the threshold of stimulated Raman scattering can be effectively improved by using linear or nonlinear passive fiber instead of constant type, and the study can provide a useful reference for the design of high-power fiber combiner and fiber end cap.