In the present work, dynamic water sorption processes in a series of poly(ether imide) (PEI) modified diglycidyl ether bisphenol A/(4,4'-diaminodiphenyl)sulfone (DGEBA/DDS) systems were investigated. The clear picture of the existing state and the diffusion process of water molecules in the blends was first elucidated by two-dimensional (2D) correlation analysis (based on attenuated total reflection Fourier transfer infrared (ATR-FTIR) measurement), and the novel technique used here could be the most effective as well as convenient way to perform the dynamic analysis on such investigations. Furthermore, by means of scanning electron microscopy (SEM), the delicate relationship between dynamic water sorption behavior and the morphology resulting from phase separation was also discussed. Two states of water as free/bound water were found in the systems, the diffusion sequence of which suggested not only composite-dependence but also morphology-dependence.