The industry is becoming more conscientious of environmental management and are promoting sustainable production. But the dyeing industry is still recognized as one of the polluting industries which discharges wastewater. Therefore, efforts are being made to reduce wastewater using ultra low liquor ratio dyeing machines and foam dyeing. However, these techniques do not solve the basic problem of wastewater generation. The supercritical fluid dyeing(SFD) technique is a new dyeing process using supercritical carbon dioxide instead of water. To dye aramid(Nomex) spun yarn by SFD, a 3 liter SFD machine was designed and manufactured. C.I. Disperse Red 360, Red 60, Yellow 54 and Blue 56 were used in this work. Dyeing property and level dyeing of aramid fiber were improved by the incorporation of in-out/out-in circulation device, nozzle, and cover in the SFD system. Physical properties(tensile strength, elongation, shrinkage) of Nomex spun yarn treated by the SFD condition(13$0^{circ}C$, 20 MPa, 60 min) were unaffected. Dyeing property of Nomex spun yarn with disperse dyes in the SFD increases as molecular weight of dyes decreases and as temperature and pressure of dyeing increases in the E type dyes. Colorfastness of dyed Nomex spun yarn by the SFD were acceptable except for wash fastness.