A ring-opening metathesis cross-metathesis (ROM-CM) hybrid polymerization strategy was developed for the synthesis of polyolefins with different topologies. By integrating the unsaturated olefin ring for ROM and the terminal olefin for CM in a single monomer, the two mechanisms could be performed simultaneously with olefin metathesis catalysts G2 and G3. In-situ NMR was used to study the reaction kinetics under various temperatures. The architecture of the polymer could be controlled by tuning the reaction temperature. The study of reaction kinetics reveals that both k(ROM) and k(CM) will decrease as the conversion increases and that the rate ratio k(ROM)/k(CM) will decrease as the reaction temperature increases, indicating that the degree of branching will increase with reaction temperature and conversion, thus providing us a useful guidance for the synthesis of polyolefins with target topologies.