Via nucleating agent (N,N'-dicyclohexyl-2,6-naphthalene dicarboxamide, short as NJS) self-assembly, dotlike, needlelike, and treelike crystallite morphologies of NJS are induced in isotactic-polypropylene (iPP) matrix. Adding NJS leads to a decrease of the viscosity of iPP, which is ascribed to the selective absorption of polymer chains with high molar mass on the surface of NJS. During steady shear test, the network of treelike NJS is deformed, resulting in the formation of numerous needlelike NJS. Under shear condition, the adding of NJS could accelerate the crystallization kinetics and enhancing the crystal orientation. More interestingly, as the morphology of NJS changes from dotlike to treelike, the crystallization kinetics and crystal orientation could be further improved. Under static condition, iPP/NJS composite with treelike NJS shows the highest β-iPP relative crystallinity (Kβ) and the largest long period. Upon uniaxial stretching, a higher Kβ could increase the voids number. However, the size of voids is similar regardless of the NJS morphology. β-α phase transition, which occurs through melting-recrystallization, takes place after void formation. No obvious orientation of polymer chains in the crystal can be found during intralamellar and interlamellar slip for both α-iPP and β-iPP. Meanwhile, in the strain range of 0.1~0.6, the c-axis of the β-iPP crystal tends to orient perpendicular to the stretching direction. This is caused by lamellae twisting, which is a unique deformation mode of β-iPP lamellae. The twisting of β-iPP lamellae could accelerate its fragmentation, which will support voids growth. Consequently, the twisting of lamellae is also proposed to be responsible for the intense voids formation of the composite with higher β-iPP relative crystallinity. At a strain larger than 0.6, the drastic increase of orientation is mainly caused by the rotation of the residual fragmented lamellae and the orientation of the newly formed crystals.