To study the propagation properties of optical soliton in optical fiber, the third-order nonlinearity effect is regarded as the small disturbance. The attempted bright soliton-like solution is obtained from modified nonlinear Schr?dinger equation (MNLS). The Lagrangian density function expression is obtained by using calulus of variational method, from which the evolution equation for the parameter of the optical soliton-like pulse evolving on the propagation distance are derived. Then the direct and indirect effects of small disturbance via a,b,ω,ξ are analyzed and discussesd. The profiles of the evolution are made by the Matlab software, which show the relation of |b| with a,ξ with β and Z,ω with β and Z,a with b and Z.