To address the bottleneck of inefficient separation between kaolinite and other clay minerals from coal slurry during flotation, this study systematically investigated flotation separation system employing kerosene as the collector, sec-octyl alcohol. as the frother, and polyglutamic acid (PGA) as the selective suppressant. Through flotation experiments combined with characterization techniques including Fourier Transform Infrared Spectroscopy (FT-IR), contact angle analysis, and adsorption capacity measurements, Experimental results indicate that in a weakly alkaline pulp environment, polyglutamic acid effectively suppresses kaolinite flotation while minimally affecting coal floatability. At pulp pH of 8 and polyglutamic acid dosage of 240 g/t, the clean coal yield reached 74.48% with an ash content of 6.47%. Contact angle and adsorption capacity tests further revealed the distinct adsorption characteristics of polyglutamic acid on coal and kaolinite surfaces. After polyglutamic acid treatment, the contact angle on kaolinite decreased from 17.76° to 5.16°, whereas the contact angle on coal samples remained essentially unchanged. FT-IR analysis revealed that the carboxyl groups in polyglutamic acid molecules undergo chemical adsorption with kaolinite surfaces, enhancing their hydrophilicity and effectively suppressing mechanical entrainment of kaolinite during flotation. This study confirms polyglutamic acid's potential as a highly effective selective inhibitor in coal slurry flotation, providing theoretical foundations and technical pathways for mitigating clay mineral interference in flotation processes and improving coal slurry separation efficiency.