Physical mechanism of supercontinuum(SC) generation in fiber was studied systematically based on nonlinear Schroedinger equation.The contributions to SC spectrum of self-phase modulation(SPM) and group velocity dispersion(GVD) were studied.And the SC generation in a conventional dispersion-shifted fiber(DSF) pumped by an actively mode-locked Er~(3+)-doped fiber laser is studied experimentally.The theoretical and experimental results indicate that SC generation in fiber depends considerably on both SPM and GVD.For picosecond pumping pulses and conventional fibers,SC generation can be described by considering the effects of SPM and second-order dispersion effects.