Crystallization dynamics and lamellar orientation are affected under the dynamic interplay between crystallization and phase separation. We carried out the experiment in a dynamically asymmetric blend of amorphous poly(methyl methacrylate) (PMMA) and crystalline poly(ethylene oxide) (PEO). If phase separation is really weak, lamellae are normally grown in the radial direction within spherulites. Growth rate shows a bell-like curve with respect to temperature. However, when strong phase separation intervenes, the growth rate curve is characterized by double peaks, one of which is dominated by crystallization and the other by phase separation. Meanwhile, lamellae tend to orient in the tangential direction in concentric alternating structures, whose formation mechanism has been explained in previous studies. This lamellar orientation inversion is reflected by a negative to positive birefringence inversion under optical microscopy. Within lamellar stacks, more amorphous molecules tend to be pushed out under the effect of phase separation, leading to smaller long period.