The polypropylene-graft-cardanol (CAPP) was prepared by reactive extrusion of polypropylene (PP), dicumyl peroxide (DCP) and cardanol. Differential scanning calorimeter, polarizing microscope and wide-angle X-ray diffraction were used to evaluate the effects of DCP and cardanol on the nucleation and crystallization of PP. Results indicated that DCP could work as crystallization nucleator for PP and cardanol could afford the impurity needed at the small angle kick pleat of lamellae during spherulite growth. For the effect of DCP on nucleation, it was found that the crystallization rate of PP was enhanced by 2 to 3 times by the addition of 0.2% DCP. For the effect of cardanol on spherulite growth, it was found that the growth rates of CAPP were increased from 10.9μm · min −1 to 13.5 μm · min −1 by the addition of 5% cardanol. Due to the nucleation effect of DCP, the total crystallization rates of degraded PP initiated by DCP at the process of reactive extrusion (dPP) and of CAPP were quicker than that of PP. Attributed to the promotion by cardanol, the spherulite grew more perfectly in CAPP than in PP, so Avrami exponents of PP increased from 2.1–2.5 to 3.1–3.5 by the addition of cardanol.