Taking into consideration of various influencing factors

it is of major significance to have an exact and computationally efficient evaluation algorithm for the variance of Four-Wave Mixing（FWM）noise to the optimal design of DWDM systems. On the basis of neglect of inter-channel crosstalk

this paper first obtains the pulse transmission law by using the dynamic splitstep Fourier algorithm and then on this basis

obtains the channel overlap functions that determine the efficiency of FWM.Calculation results of examples show that FWM efficiency is to a certain extent related to the pulse variations in the course of propagation:when group-velocity dispersion coefficient is relatively small

the normalized characteristic width is relatively large and when the peak-power of the incident pulse is relatively large

the correlation degree is large

and that when the chirping coefficient is positive and large and the propagation rate is relatively high

the effects of pulse variations with the propagation distance on FWM efficiency cannot be neglected.