The pursuit of ordered two-dimensional (2D) materials with customized properties has fueled extensive research. While many established fabrication methods rely on substrates, solution-based polymer self-assembly processes remain much unexplored. Here, by manipulating the delicate balance between dominating and competing forces, we demonstrate how polymer chains fold, self-adjust, and self-assemble into diverse ordered 2D nanostructures in solution guided by an energy landscape, especially highly ordered crystalline structures, which are of great challenge to realize by polymers. An alternating copolymer initially self-assembled into 2D planar flakes via a kinetic pathway, lacking crystallinity. Through thermal annealing, they overcame a local kinetic barrier, in situ transforming into 2D circular crystalline clusters. Furthermore, by facilely replacing alkenyl linkers with triazoles in the alternating copolymers, additional tunable competing interactions were introduced, enabling the system to take thermodynamically favored pathways from the beginning and form 2D crystalline spindles directly. Besides, both the systems exhibited reversible self-assembly behavior and remote-controllable merit under light irradiation, forming 2D crystalline structures including flowers and spindles, respectively, highlighting the systems’ responsiveness and versatility. This study offers diverse and facile strategies for constructing and fine-tuning tailorable nanostructures, suggesting promising applications in precision engineering and biomedical technologies.