The problem of step length in the numerical simulation of laser beam propagation in atmospheric turbulence along slant path is studied.For boundary reflection under large step length in split-step Fourier algorithm,numerical experiments for absorbing boundary method are carried out,and the upper bound of the step length is obtained.The filter function method is proposed to further release the limit for the step length.The effectiveness of filter function method and its effective region are proved by the beam propagation simulation in vacuum.Combining these two methods,a setting way of phase screen on slant path is given.The propagation of laser beam on this path is simulated,and the coherence length and scintillation index of the laser spot are calculated.The numerical results are in good agreement with the theory,which proves that the filter function method can effectively increase the upper bound of the step length in the slip-step algorithm,thus improving the simulation efficiency of laser beam over long range transmission in atmospheric turbulence.