Self-assembly of copolymers in solution is a promising way to prepare novel materials. An accurate control over the self-assembly of copolymers in solution requires a profound understanding about the related thermodynamic rules and kinetic mechanisms. Theoretical modeling and simulation play an increasingly important role in characterizing the structure details and the formation process of polymer assemblies. In this review, we first introduce theoretical modeling and simulation methods that have been applied to investigate the self-assembly of copolymers in solution, including particle-based methods, field-theoretical methods and hybrid modeling methods Then, the application of these methods for the self-assembly of linear block copolymers in solution is highlighted, including the thermodynamic rules and kinetic mechanisms underlying the formation of self-assembled structures. Furthermore, the simulation works of the self-assembly of branched copolymer systems, including graft copolymers, star-like copolymers, dendritic copolymers and bottle-brush copolymers, are addressed. In addition to the one-component polymer systems, simulation investigations of polymer mixture systems are discussed, both the polymer/polymer systems and polymer/nanoparticle systems are considered. Finally, perspectives on the theoretical modeling and simulation in the field of self-assembly of copolymers in solution are presented in the section of concluding remarks and outlook.