In this paper, a simulation discussing the cause inducing the anisotropy of hydrogen cluster expansion is implemented by using LAMMPS tool for the molecule dynamics simulations. Through analyzing the behavior of electrons contained in the cluster and the variations of distance between outermost protons of all directions and cluster center with time, we clearly find that the expansion of hydrogen cluster is anisotropic, which is due mainly to the anisotropies of the quiver and escaping of electrons. Then we study the evolutions of proton energy component and anisotropic degree, and find that the anisotropic degree first increases with laser electric field increasing, then decreases gradually to a stable value greater than one. Additionally, we analyze the relationship between observation angle and average proton energy from hydrogen cluster irradiated by ultreshort laser pulse, and find that our simulation results accord with the experimental results qualitatively.