The creation and characterization of laser-generated plasma are affected by laser irradiance, representing significant phenomena in many applications.  The present work studied the spectroscopy diagnostic of laser irradiance effect on Zn plasma features created in the air by a Q-switched Nd: YAG laser at the fundamental wavelength (1064nm).  The major plasma parameters (electron temperature and electron density) have been measured using the Boltzmann plot and the Stark broadening methods.  The value of electrons temperature ranged from 6138–6067 K, and the electron density in the range of 1.4×10¹⁸ to 2×10¹⁸ cm^-3, for laser irradiance range from 2.1 to 4.8×10⁸ (W/cm²).  The McWhirter criterion for preserving a local thermodynamic equilibrium (LTE) condition is confirmed in this study.  Furthermore, other fundamental plasma parameters, such as Debye length (λ_D), number of particles in Debye sphere (N_D), and plasma frequency (ω_p), were measured. We found that all plasma parameters are affected by laser intensity.