A simple computer algorithm for propagution of ultraghort optical pulse in optical fiber is presented in this paper. Frequency modulation, spectrum broadening and square pulse pulse shaping are obtained for optical fiber with positive dispersion and the propagation of soliton wibh N = 1, 2 and 3 is obtained for a fibe with negative dispersion. The calculated results with this algorithm are well in agreement with that calculated by nonlinear Schrodinger equation.