Single-walled carbon nanotubes (SWNTs) were synthesized with a high growth rate by an arc plasma method employing the electrodes made from a Ni-Y mixture catalyst. In a previous study, it was reported that the monitoring of high-crystallinity SWNT growth enabled the evaluation of the results of the optical emission spectroscopy (OES) of C-2, Ni, and Y. Here, the impact of helium pressure of arc plasma on the high crystallinity of SWNTs was determined by considering the high intensity ratios of catalytic metals over C-2 emissions at low helium pressures in the arc plasma (C) 2018 The Japan Society of Applied Physics.