To describe the parameters of a big format Charge Coupled Device (CCD) by a function with definit physical meaning and to evaluate its radiation response performance directly, a concept of “radiation response function matrix” was proposed to describe the radiation response parameters of each pixel of the CCD. Firstly, by analyzing the physical concept of each element, some parameters such as absolute radiate response, nonlinearity, dark noise, Signal-to-Noise Ratio (SNR) and the non-uniformity of each pixel of the CCD were characterized by the matrix. Then, response characteristic coefficient of each pixel was obtained using the model of multiple regression analysis by a test on the area CCD KAI-16000. Finally, by taking the result for an example, application of this matrix was discussed. Experimental results show that the response of this CCD is linear, and its non-uniformity is 3.1%, dark noise is 3.84. These results demonstrate that the method is feasible and practical, and it can satisfy the requirement of the description of a big format CCD.