The branch point problem was computed by four-dimension code of laser propagating in atmosphere and compensation of adaptive optics in this paper. The relation of density of branch point with atmospheric turbulence and propagating range was analyzed. The problem of branch point of various beacon and its effect on compensation of adaptive optics were analyzed too. These computational results showed that the compensative effect of adaptive optics is not characterized completely by coherence length and frequency bandwidth of adaptive-optics system. The effect of scintillation needs to be considered in compensation of adaptive optics when a laser beam propagated over a long distance through even weak atmospheric turbulence.