The evolution equations for the parameters of Gaussian pulse with propagation distance in optical fibers is derived, considering high-order dispersion and the fifth-order nonlinearity by means of variational method from the modified nonlinear Schrdinger (MNLS) equation. Then, the relations between amplitude and width, frequency and chirp, width and chirp are obtained. The analytical solution about the pulse width and pulse center evolution on the propagation distance is obtained. The graph of the pulse width evolution with transmission distance is described. The results show that the high-order dispersion and fifth-order nonlinearity in fiber will affect Gaussian pulse parameters of evolution, but the adiabatic relation between the pulse width and amplitude has not been changed. High-order dispersion causes the compression of Gaussian pulse width spread, and the fifth-order nonlinearity causes Gaussian pulse width, which may offset the pulse width or the influence of the initial chirp in a certain degree, and thus realize the conformal pulse transmission.