Abstract Picosecond laser pulse propagation in monomode optical fiber is demonstrated and investigated by numerically simulation in this paper. The numerical simulation is done by nonlinear Schr?dinger equation with the aid of Mathlap program. The results show that self phase modulation (SPM) leads to broadening the spectral width from 5nm to 38nm after 50m of the fiber length and accompanied by temporal broadening in the pulse width.