ABSTRACT This study examines the impact mechanism and dynamic changes in how reports on the discharge of nuclear‐contaminated water in Japan affect Chinese consumers' willingness to purchase seafood. An extended theoretical model is innovatively constructed by integrating the variables of media involvement and risk perception, based on the Theory of Planned Behavior (TPB). A longitudinal research design was employed, utilizing a mixed‐method approach that combines Structural Equation Modeling (SEM) and Fuzzy‐set Qualitative Comparative Analysis (fsQCA). The SEM results indicate that the influence of media involvement on risk perception significantly weakens over time. The relationship between risk perception and attitude shifts from negative to positive, while the impact of subjective norms on purchase intention strengthens over time. The fsQCA results reveal diverse antecedent configurations affecting purchase intention at different periods, highlighting the nonlinearity and complexity of consumer decision‐making. This study provides new insights into understanding the dynamic evolution of consumer behavior in response to public emergencies, while also expanding the applicability of the TPB in this context. The findings have important practical implications for government crisis communication strategies and corporate marketing strategies.