Silicon nitride ceramics were irradiated by a solid-state Nd3+: YAG pulsed laser with an output wavelength of 1064nm. The plasma characteristic spectral lines were obtained by changing the laser energy. According to the National Institute of Standards and Technology (NIST) standard atomic spectroscopy database, the spectral lines were identified. The full width at half maximum parameters of Si I 252.27nm and Si I 288.60nm neutral atom characteristic lines of the spectral lines were obtained by Lorenz and Gauss fitting, respectively. Using the Stark broadening method to calculate the electron density, it was found that as the laser energy increases, the electron density gradually decreases. When the laser energy was increased to 156mJ and reached the minimum value, the electron density began to increase as the laser energy continued to increase. The reason for conducting the analysis is that as the plasma shielding effect increases with the increase of laser energy, the plasma absorbs the laser energy by reverse bremsstrahlung and resonance absorption mechanism. The decrease in energy irradiated onto the target, which excites the amount of plasma to reduce the plasma density. When the laser energy is raised to 156mJ, the energy irradiated to the target and the energy of the plasma shield are dynamically balanced. At this point in time, the electron density reaches a minimum, and the electron density increases with increasing laser energy.