A novel aligned carbon nanotubes (CNTs) gas sensor based on gas discharge has been achieved. The sensor was composed of aluminum cathode electrode, insulated film and CNTs anode electrode. Due to adopting the method of anodic aluminum oxide (AAO) template to grow aligned CNTs, the electrode and CNTs were integrated, so the gas sensor simplified its structure and processing technics. As different gases have their unique breakdown voltage and discharge current, it is possible to identify one gas or certain mixture gases. Experimental results showed that the CNTs gas sensor proposed in this paper had the merits of small size, fast response, good sensitivity and selective, and it was very easy and convenience to be operated at normal temperature and atmosphere pressure, so it had the practical value.