Dissipative particle dynamics simulations are performed to investigate the self-assembly of rod-coil diblock copolymers RNRCN-NR within a rod-selective slit. The self-assembled structure of the confined system is sensitively dependent on the rigidity k(theta) and the fraction f(R) of the rod block and the slit height H. From the phase diagram of structures with respect to k(theta) and f(R) for N = 12 and H = 6, we observe four main structures including disordered cylinder (DC) structure, hexagonally packed cylinders (HPC) perpendicular to the slit surfaces, and lamellar structures parallel (L-parallel to) and perpendicular (L-perpendicular to) to surfaces. And structure transitions can be achieved by tuning k(theta). The effect of the slit height on the self-assembled structure is also studied for R6C6 and R7C5 copolymers with large k(theta). For R6C6, different structures near surfaces and in the interior of slit are observed in relatively wide slits. Whereas for R7C5, L-perpendicular to structure, whose lamellar domain spacing decays exponentially with H, is generally generated. Our results suggest an effective way to control the ordering of rod-coil diblock copolymers under nanoscale confinement.