Using first-principles theory, we investigated the adsorption performance of CoN4- CNT towards six small gases including NO, O2, H2, H2S, NH3, and CH4, for exploiting its potential application for chemical gas sensors. The frontier molecular orbital theory was conducted to help understand the conductivity change of the proposed material at the presence of gas molecules. The desorption behavior of gas molecules from CoN4- CNT surface at ambient temperature was analyzed as well to determine its suitability for sensing application. Results show that CoN4- CNT is a promising material for O2 and NH3 sensing due to their desirable adsorption and desorption behaviors while not appropriate for sensing NO due to the poor desorption ability and for sensing CH4 and H2 given the poor adsorption behavior. Our calculation would provide a first insight into the CoN4- embedded effect on the structural and electronic properties of single-walled CNT, and shed light on the application of CoN4- CNT towards sensing of small gases.