Miscible polymer blends offer great designability on shape memory effect (SME) with adjustable mechanical properties and stimuli-responsiveness, by simply changing the constituent compositions. However, the thermodynamics understanding behind those SMEs on miscible polymer blends are yet to be explored. This paper describes an approach to achieve highly designable SMEs with adjustable glass transition temperature (Tg) and width of glass transition zone by dynamically coordinating components in miscible blends. An extended domain size model was formulated based on the Adam-Gibbs theory and Gaussian distribution theory to study the synergistic coordination of component heterogeneities on conformational entropy, glass transition and relaxation behavior of the miscible blend. The effectiveness of model was demonstrated by applying it to predict dual- and triple-SMEs in miscible polymer blends, where the theoretical results show good agreements with the experiment results. We expect this study provide an effective guidance on designing advanced miscible polymer blends based on the SME.