Based on the standing-wave theory, a modified method is proposed to separate interface and volume absorption in HfO2 single layers. HfO2 single layers with multiple half-wave optical thickness were prepared; in such case, the electric field at air-film and film-substrate interface is equal, and total absorption from both interfaces can be easily expressed by the product of electric field intensity and a simplified total interface absorption coefficient. Ultralow-absorptive substrates were used to eliminate the contribution of substrate absorption. When HfO2 single layer was irradiated from the coated and uncoated side in the photothermal measurement, two equations were obtained and utilized to separate the interface and volume absorption. The validity of our method was further confirmed using another thickness changing approach. By contrast, irradiation direction changing method is better because only one sample is required.