Abstract: The uniformity of optical thin films has become quite vital because large diameter optical devices are used widely. In this paper, according to the basic theory of photothermal detuning technique, with Visual Basic 6.0 to write control program, the experiment system for measuring the absorption uniformity of optical films was designed and built for the first time. Absorptions at the different points on the sample surface were measured, and the surface absorption image of the sample was made. The result shows that the designed experimental system which is stable and accurate can be used to absorption uniformity measurement of optical thin films, and the automated measurement in the whole system is achieved. The designed system which provides experimental foundation for the advancing application of the photothermal detuning technique is feasible.