This study investigates the effect of parallel plate confinement on the spectra of the CN molecule in laser-induced PMMA plasma in the atmospheric environment. The wavelength of five measured spectral peaks are 388.29 (0-0), 387.0 (1-1), 386.14 (2-2), 385.44 (3-3), and 385.03 nm (4-4). The experimental results show that the spectral peak intensity of the CN molecule with spatial confinement is stronger than that without spatial confinement. Moreover, the vibrational temperature of the CN molecule is calculated by fitting the CN spectra. The calculated vibrational temperature of the CN molecule with spatial confinement is higher than that without spatial confinement, and the vibrational temperature at high laser energy is higher than that at low laser energy. The shock waves reflected by the parallel plate compress the plasma plume and increase its temperature and number density. Thus, the spectral intensity of the CN molecule in laser-induced PMMA plasma is improved.