Abstract: During the investigation of polymer dielectrics, flat responses which overleap large temperature and frequency ranges can be found in various low loss dielectrics. It cannot be demonstrated by the current theoretical models such as Dissado-Hill model, resulting in the dilemma of data processing and analysis. Therefore, the dielectric response of biaxially-oriented polypropylene (BOPP) over broad temperature and frequency ranges are measured, which is widely used in film capacitors. The existence of flat dielectric response is confirmed, with its general conditions and features being demonstrated. Besides, the numerical analytical method is proposed towards flat dielectric response, validated by the quantitative decoupling of the dielectric response of BOPP film. The method proposed is compatible with the current Dissado-Hill model, thus increasing the feasibility significantly. Furthermore, according to the analysis of microscopic dipolar screening, the physical interpretation of flat dielectric response is proposed, based on which the scope of method is specified.