Abstract: Accurate quantitative diagnosis of pulsed radiation fields, particularly soft X-rays, relies heavily on the linear response of detection materials. Plastic scintillators are widely employed in such diagnostics, especially for inertial confinement fusion (ICF) research, owing to their high luminous efficiency and fast temporal response. However, these scintillators exhibit a significant nonlinear response under high-dose-rate soft X-ray irradiation which limits their accuracy and utility. The saturation effect mainly affects in quantifying radiation power of intense pulsed radiation fields. Consequently, detailed experimental and theoretical studies on the saturation power limits of scintillation detection systems utilizing plastic scintillators are essential. While substantial research has been conducted internationally on the nonlinear responses of inorganic scintillation crystals, such as CeF₃ and LYSO∶Ce, investigations focusing specifically on the underlying dose-rate nonlinear exciton dynamics within plastic scintillators under intense pulsed soft X-ray radiation remain relatively limited. Addressing this critical gap is the primary objective of this study. The research methodology combined theoretical modeling with experimental validation. Building on the established framework of exciton concentration quenching models used for inorganic scintillators, detailed exciton dynamics modeling and analysis were performed to elucidate the mechanisms of nonlinear response during the luminescence of organic plastic scintillators. This theoretical approach provided a specific prediction for the nonlinear response threshold of the plastic scintillator EJ-214 under high soft X-ray dose-rates. Subsequent experimental verification was carried out. Samples of plastic scintillator EJ-214 were subjected to the intense pulsed soft X-ray radiation field generated by a Z-pinch facility. Precise measurements of the scintillator’s light output at different incident power densities enabled the accurate determination of the energy flux density threshold corresponding to the onset of measurable nonlinearity. The energy flux density threshold corresponding to a 10% nonlinear response of the plastic scintillator EJ214 under pulsed soft X-ray irradiation is measured as 1.68×10⁵ W/cm². Crucially, this experimentally determined threshold demonstrates excellent quantitative agreement with the theoretical prediction of this model. A key result of this work is the successful quantification of the nonlinear response threshold for plastic scintillator EJ-214 under high-dose-rate soft X-ray irradiation. Furthermore, the established theoretical exciton dynamics model exhibits significant predictive power and broad applicability. By substituting the intrinsic parameters characteristic of different exciton-type scintillators, such as organic plastic variants or inorganic crystals, into the model framework, it is now possible to predict their specific dose-rate nonlinearity thresholds. This predictive capability is a key outcome with considerable practical value for the field of quantitative pulsed X-ray diagnostics. It provides essential guidance for the selection of appropriate scintillator materials with a sufficient linear dynamic range for specific high-intensity applications, guides the design of future diagnostic systems, and supports the development of potential correction strategies to mitigate saturation effects, which can enhance the reliability of radiation power measurements in demanding environments like ICF experiments and Z-pinch research.