Silicon nitride ceramics have excellent properties of corrosion resistance, wear resistance and resistance to high-low temperature impact, which are commonly used in thermal protection materials of hypersonic vehicles. The laser weapons are the main technical means for intercepting and striking the hypersonic targets in the future. The Nd³⁺:YAG solid-state pulsed laser was used as an irradiation source and hot-pressed sintered silicon nitride ceramic was used as the target. Meanwhile, the echelle grating spectrometer was used as the detector to construct an experimental system. The radiation spectra of the target with a laser wavelength of 1 064 nm, pulse width of 15 ns, and different energies (50 mJ~500 mJ) were collected. Line identification was based on the national institute of standards and technology (NIST) atomic spectrum database. According to the Boltzmann method, the plasma electron temperatures range from 6 203 K~6 826 K, the plasma electron density range calculated by the Stark broadening method is 8.40×10¹⁵ cm^-3~1.14×10¹⁶ cm^-3, and the electronic oscillation frequency is 8.23×10¹¹~9.58×10¹¹ Hz. With the increase of laser energy, the electron temperature demonstrates an overall upward trend, and the change of electron density fluctuates.