A pulsed laser photothermal detuning technique, in which the temperature induced spectral shifts of optical coatings are used to measure photothermal signal, is presented. A theoretical model is developed to describe the pulsed laser photothermal detuning signal. The application to the absorption measurement of optical coatings is discussed. An experiment is performed with a highly reflective (HR) coating used in 532 nm. The amplitude and temporal behavior of the pulsed laser photothermal detuning are detected at 632.8 nm, and their dependences on the experimental parameters, such as the energy density of the excitation beam and the relative position between the excitation and probe beams on the sample surface are investigated. The results show that the detuning signal increases firstly and then decreases with the time, rises with the increase of the power density, and reaches the maximum at the position where the pump and probe beams are overlapped.