Self-assembly of copolymer is an important approach to obtain multifarious nanostructures. Polymerization-induced self-assembly (PISA) is a recently developed and powerful copolymer self-assembly strategy. However, some researchers have reported a different morphology prepared by PISA and the traditional copolymer self-assembly using the same copolymer system. In this work, to explore the mystery, we develop a precise mesoscopic dissipative particle dynamics (DPD) model to reveal insights into the PISA of poly(4-vinylpyridine)-b-polystyrene (P4VP-b-PS). It is observed that P4VP-b-PS nanotubes can be obtained via TSA rather than PISA, which is consistent with reported experimental results. By carefully investigating the dynamics of PISA under specific solvent and monomer conditions and different polymerization rates, we propose that combining excessive monomers with multistep PISA can help to enhance the morphological regulation ability of PISA and retain a high solid content simultaneously. The findings in this study not only provide a precise modeling method for investigating copolymer self-assembly but also serve as a rational guide for future studies toward optimization of the PISA strategy.