For the application of long-distance laser ranging, such as geosynchronous satellite laser ranging and lunar laser ranging, the uplink beam is simulated by using split-step numerical method (or fast-Fourier-transform beam propagation method). Using unequal interval phase screen distribution according to the profile of atmosphere structural constant, the average propagation intensity is in good agreement with theoretical value. Based on this, the effect of beam wander is analyzed, which is the main reason of intensity decrease on axis. So after the removal of beam wander, without pointing error, the intensity on axis increases roughly. This improves the probability of detecting echo of laser ranging. It is found that there is a proper initial beam waist to minimize the on-axis scintillation index. The simulation results are very useful to the design of tip-tilt correction system.