Polymer blending is an easy and effective way to obtain new materials with desired properties. However, most polymers are immiscible due to the huge difference in molecular structure, leading to various morphologies. The properties of immiscible polymer blends are highly dependent on the morphology formed during processing. For polymer blends, one of the challenges is that the generated morphologies during processing are usually in a non-equilibrium state and morphology coarsening, via coalescence, breakup and retraction, was found by a lot of researchers when polymer blends were subjected to thermal annealing in quiescent conditions or second processing, which led to a huge increase in phase size. The effect of nano-silica particles on the morphological evolution of Polypropylene (PP) / Polystyrene (PS) blend is evaluated. An obvious coalescence of the dispersed droplets was found for the pure blend when annealing in the melt state. The nano-silica particles were found to be selectively dispersed in PS phase. With the addition of nano-silica particles, the coalescence was found to be slowed down, no matter where the nano-silica particles were in, in the matrix, in the dispersed phase or at the interface. For blends filled with 8wt% nano-silica particles, the coalescence was almost totally suppressed. We think that the shape relaxation of the dispersed phase is owing to the molecular relaxation and the retarded molecular relaxation because of nanoparticles or even the particle network finally suppressed the shape relaxation of the dispersed phase in immiscible polymer blends.