Bottlebrush polymers are a class of comb polymers that have the unique side chain structures and properties. Functional bottlebrush polymers have found broad applications in photonic crystals, surfactants, pharmaceutical carriers, antifouling coatings and smart materials. The synthetic strategies to bottlebrush polymers by ring-opening metathesis polymerization (ROMP) exhibit various advantages, such as simple synthesis steps, high polymer graft density and uniform side chain composition. Well control of polymer composition, molecular weight and molecular weight dispersity could be achieved by ROMP. This review summarizes the synthesis of homo, block, Janus, core-shell bottlebrush copolymers via ROMP. Moreover, the advances in finely controlling the bottlebrush polymer architecture are discussed.