Gas sensors based on Carbon Nanotube (CNT) can be used to detect harmful environmental pollutants. Also, CNT has some unique electrical properties as gas sensor application. In this research, we have presented a new structure that is constructed from joining two similar Folded Armchair Graphene Nanoribbons (FAGNRs). Two FAGNRs are joined from their open sides, which make a CNT like device with noncircular cross section and we call it Attached FAGNR tube (AFAGNT). In addition to the physical properties we have investigated gas sensing performances of CNT and AFAGNT in presence of CO, O-2 and CO2 gases molecules. In this regards, our simu-lation results of AFAGNT show different significant sensitivities to CO gas molecule at various bias voltages, especially at 0.8V. On the other hand, CO2 gas molecule doesn't adsorb onto the AFAGNT which means it is not a CO2 gas sensor.