The dependences of the signal pulse average power and gain coefficient on the distance are obtained by using the rate equations and power propagation equations,and the Ginzburg-landau equation is employed to study the propagation of the ultrashort pulse.The results show that parameters suchlike signal pulse average power,energy and gain coefficient are not susceptible to the dispersion and nonlinear effect,while signal pulse peak power,and the characteristics of time and frequency domain are easy to be affected by the dispersion and nonlinear effect.The instability of pulse width caused by pulse splitting and broadening and the effect of the instability on pulse propagation are analyzed and discussed under the consideration of the nonlinear effect.It reveals that the accuracy of numerical simulation can be improved by introducing the pulse width instability in the study of the pulse propagation.