Based on MNLS,by using the method of variational principle,the influence of fifth-order nonlinearity on the propagation of soliton-like pulses in fiber is investigated,the evolution equations for the parameters are deduced,the relations between width and distance,chirp and width,are calculated and the evolution equations for frequency and phase are studied by using Runge-Kutta algorithm. The result indicates that five-order nonlinearity compresses the width and has little influence on frequency and phase,so appropriate nonlinearity(γ=0.0001～0.01)is helpful to steady transmission of soliton-like pulses in fiber.