A simplified two-dimensional plasma hydrodynamic modal of X-ray laser on slab target is proposed on the basis of self-similarity method. The properties of two-dimensional hydrodynamics of X-ray laser plasma are studied using the model. It is shown that after the action of driving laser, the electron temperature and the electron density along the focus line will tend to equibrium with elapse of time. This result has an important meaning in the optimized design of the experiment on the X-ray laser.