In order to develop high-performance CNT-based electronic and optoelectronic devices, it is crucial to establish the relationship between the electron transport properties of carbon nanotubes (CNTs) and their structures. In this work, we have investigated the transport properties of chiral (8, m) and (10, m) CNTs sandwiched between two gold electrodes by employing nonequilibrium Green's function (NEGF) combined with density functional theory (DFT). We demonstrate that with the change of chirality the transport property changes, as predicted by the (n - m) rule. The change of length is also considered. Our results show that the electrical conductance of (10, m) CNTs is larger than that of the (8, m) CNTs, due to larger diameter. Furthermore, we found that the (8, 1) chiral CNT does not follow the (n - m) rule in shorter length and it shows metallic behavior. The cohesive energy, wavefunctions of electronic states, and coupling energy calculation indicate that the devices considered in this study are stable. The transmission spectra, current vs. voltage curves, and transmission eigenchannels provide strong evidence for our findings. Among the (10, m) series, (10, 3) CNT would be the optimal choice for a semiconducting molecular junction device with a significant conductance of 20 μA at 0.8 bias voltage.