Polymer blends offer an exciting material for various potential applications due to their tunable properties by varying constituting components and their relative composition. Our simulation results unravel an intrinsic relationship between the phase behavior and crystallization characteristics with the relative composition of A- and B-polymer in the system... We report simulation results for non-isothermal and isothermal crystallization with weak and strong segregation strength to elucidate the composition dependent crystallization behavior. With increasing composition of low melting B-polymer, macrophase separation and crystallization temperature changes non-monotonically, which is attributed to the change in diffusivity of both the polymers with increasing composition of B-polymer. In weak segregation strength, however, at high enough composition of B-polymer, A-polymer yields relatively thicker crystals, which is attributed to the dilution effect exhibited by B-polymer. When B-polymer composition is high enough, it acts like a solvent while A-polymer crystallizes. Under this situation, A-polymer segments become more mobile and less facile to crystallize. As a result, A-polymer crystallizes at a relative low temperature with the formation of thicker crystals. At strong segregation strength, dilution effect is accompanied with the strong A-B repulsive interaction, which is reflected in non-monotonic trend of mean square radius of gyration with increasing composition of B-polymer. Isothermal crystallization reveals a strong relationship between composition and crystallization behavior. Two-step (viz., sequential crystallization) yields better crystals than one-step (viz., coincident crystallization) for both the polymers. (read more)