Analysis of the thermal gas lens in the discharge tube of a self-heated copper vapor lasers (OVL) is given. For the different schemes of copper vapor laser, it has been found that the steady-state OVL can be equivalent to a convex lens or a concave lens. As results of the experiment, the relations between the focal length of the thermal gas lens and the input power and buffer gas pressure are presented. The evolution process of the thermal gas lens from concave to convex lens is described.