A new finite difference wide-angle beam propagation method is developed by introducing the least-squares expansion approximant in the propagator expansion- In this new method it is not necessary to select the reference index point because of the whole region approaching the lease-square expansion- This method avoids the problems induced by error selection of the reference index in the old methods based on Taylor or Padè expansion- Several typical structures are simulated by the new method and the results prove the validity of it-