Focusing in photonic crystal (PC) slab has been studied theoretically and experimentally. PCs are composed of a unit cell repeated periodically. In this article, we investigate in detail the influence of the continuous rotation of the unit cell on the focus in a two-dimensional photonic-crystal-based flat lens by the finite-difference time-domain method and experimental measurement. It is found that the focusing can appear within a large range of rotated angle of the unit cell. When the rotation exceeds a certain angle, the focusing disappears. However, it is interesting that the focusing does not depart from the symmetric center because of rotation of the unit cell.