Dissipative particle dynamics (DPD) simulations were used to study the self-assembly behavior of polymer brushes with rod-coil backbones, polycaprolactone-b-poly(2-(dimethylamino)ethyl methacrylate)-grafted cellulose nanocrystals (CNC-g-PCL-b-PDMAEMA), and to further examine the influences of polymer concentration, rod-block proportion and distribution of backbones and the grafting density of side chains on the resulting aggregate conformations. We proposed the "rod-coil competitive mechanism" for the self-assembly of polymer brushes with rod-coil backbones. The results indicated that the micellar structures mainly depend on the relative intensity between the orientational ordering of rod blocks and the disordered packing of the flexible blocks. The cylindrical micelles were formed when the orientational order of the rod blocks predominates, while the disorder of the flexible blocks contributes to the formation of spherical micelles. We further proved that the competitive relationship is affected by polymer concentration, rod-block proportion and distribution of backbones and the grafting density of side chains. The increasing rod-block proportion, the rod-coil-rod backbones and the asymmetric grafting side chains are beneficial to the orientation order of the brush-like polymer in the self-assembly process, thereby inducing the formation of the cylindrical micelles. The self-assembly mechanism of the rod-coil copolymer proposed in this study provides guidance and a theoretical basis for the design and regulation of novel and complex polymer aggregates.