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We constructed a new ab initio potential energy surface (PES) for CO–N2O which includes the intramolecular Q3normal coordinate for the N2O ν3antisymmetric stretching vibration. The intermolecular potential was evaluated employing the supermolecular method at the [CCSD(T)]-F12a level, with the aug-cc-pVTZ basis set plus bond functions. By integral over the intramolecular Q3coordinate, we obtained the vibrationally averaged PESs for the CO–N2O system in the ground and ν3excited states of N2O. Each PES features one nearly T-shaped global minimum and one skewed T-shaped local minimum. Based on these obtained PESs of CO–N2O, the radial discrete variable representation/angle finite base representation method and the Lanczos algorithm were applied for the calculations of bound states and rovibrational energy levels. The calculated ν3vibrational band origin shift of the N2O monomer in CO–N2O is 2.7570 cm–1, matching well with the observed value of 2.9048 cm–1. The computed microwave and infrared transition frequencies, as well as the rotational parameters, are consistent with the experimental observations.