We present the results of our recent developments of multiscale modelling on dynamics of phase separation and phase transition in multiphase dense polymeric systems. Our modeling is based on density functional theories of polymeric systems, such as the self-consistent field (SCF) theory and the Ginzburg-Landau (GL) theory. We combine these theories with flow dynamics, diffusion dynamics, and the effects of external fields such as a flow field, electric field, and confinements.