We investigate the random wandering behavior of optical vortex over propagation distance of 5km in weak turbulence. The multiple random phase screen simulation method and vortex extracting method are utilized to calculate the optical vortex positions (x,y) on the receiver plane. Numerical results reveal that x and y are Gaussian random variables. However, the errors of Gaussian fitting become larger and the Gaussian fitting curves become broader as topological charge of optical vortex increases through the same atmospheric turbulence. Our results are crucial for free-space optical vortex communication.