Propagation of femtosecond pulse and supercontinuum generation in silicon waveguide are investigated numerically by solving the generalized nonlinear Schrdinger equation. The effects of dispersive effect and nonlinear loss on supercontinuum generation are simulated and analyzed. It is found that soliton fission is the main mechanism of supercontinuum generation in silicon waveguide. The relative position between the central wavelength of femtosecond pulse and zero-dispersive wavelength (ZDW) of silicon waveguide significantly affects the generation of supercontinuum. When the input pulse falls in the anomalous dispersion regime, soliton fission phenomenon is most obvious. It is also found that the high-order dispersion plays an important role in supercontinuum generation. When the absolute value of third-order dispersion is smaller, a broader supercontinuum can be obtained. Besides, two-photon absorption (TPA) effect in silicon induces high loss, and reduces the spectral width of the supercontinuum.