The greatest SPR achieved in angle of 45.1 𝑜 at 50𝑛𝑚 of gold.  The perfect region of SPR for the gold layer was in the range (40 − 50)𝑛𝑚.  SPR for gold/air depends on incident angle, refractive index, or dielectric medium and thickness.The coherent oscillation of electrons at contact among a dielectric and metal when the metal is exposed to incoming plasmon is known as "surface Plasmon resonance". To achieve the best surface plasmon resonance (SPR) signal, several aspects must be considered, including the excitation wavelength, the sort of metals used, and the thickness of the metal layer. The modification of the surface plasmon resonance (SPR) depending on the thickness of metallic gold was investigated in this study. The reflection spectrum is determined as a function of metal thickness and dielectric medium (air), which is fixed in this case, and measuring the resonance angle for each size (length of the gold layer) to visualize the influence of the metal film on the resonance angle. The analysis concentrated on the impact of gold layer thickness variations on resonance angle shift. SPR's ideal thickness was discovered to be 45-50 nm. We used the spin coating method to create a thin layer. The thickness of thin films is measured by scanning the sample with an atomic force microscope (AFM) tip. The optimum SPR angle profile with the minimum amount of reflection and dip reflection is achieved with this film thickness. The reflectance and resonance angle performance features of gold layers were analyzed utilizing plasmonic Kretschmann configurations at a wavelength (632.8 nm) in sensing media (air). In an experimental analysis of the improved surface plasmon resonance characteristics of the gold/air coupling, they also showed a significant shift in resonance angle due to the film thickness variation. Biomedical science, optics, biosensing, and medicine are just a few of the domains where the (SPR) has been applied.