By use of molecular dynamical simulations, liquid crystal phase transitions and phase separations are investigated on the mixture of hard rod-like molecules and hard spherical molecules. Our model for the rod-like molecule is supposed to be a linear chain of 7 hard spheres connected with strong springs. We demonstrate that randomly added spherical molecules generally incline to diminish their orientational ordering. Specially in the smectic phase we have found that these mixing causes a phase separation, where the smectic rod-rich layers and sphere-rich layers are alternatively stacked in the low concentration of spheres. In the higher concentration they show 'domain phase: where the clusters of rod-like molecules are dispersed in the sea of spherical molecules, like a phase separation.