When simultaneous iterative reconstruction technique(SIRT) was applied in the near-surfacing structure
there was the problem of over-adapting in it.It was because that coefficient metrice A was not fit for the travel time Δt.The paper analyzed the limitation of SIRT and presented an improved method to weigh the travel time residual by the distance d from the source to the receiver.The calculating results showed that the method could solve the shortage and get better reconstruction images.