Laser-induced breakdown spectroscopy (LIBS) has good capability for detecting molecular spectroscopy. Currently, little research has been done on enhancing this capability by depositing nanoparticles on the surface of samples. In this paper, a pulsed Nd:YAG laser with a wavelength of 1064 nm was utilized to excite polymethyl methacrylate (PMMA) targets and generate PMMA plasmas, and five spectral peaks (0−0), (1−1), (2−2), (3−3), and (4−4) of B2Σ+ − X2Σ+ (Δν = 0) transitions of CN molecules were obtained. The CN molecule was produced by the chemical reaction (C + N → CN) between the C atoms in PMMA targets and the N2 in the air. The effect of nanoparticles on the spectral intensity and spectral stability of CN molecules was studied. And the vibration temperature of CN molecules was calculated by fitting the CN spectra. The results showed that nanoparticles could improve the spectral intensity, stability, and vibrational temperature of the CN molecules, revealing the potential of nanoparticles for enhancing signal intensity and improving analytical sensitivity in molecular LIBS.