To investigate the mediating role of the activation degree of arginine-proline metabolism in the association of coal dust and decreased lung function. CDE represented coal dust exposure, while the Hyp/Arg in BALF gauged arginine-proline metabolism activation. Pulmonary function indicators, including FVC%pred, FEV1/FVC%, and FEV1%pred, DLCO%pred, P(A-a) O2 and 6MWT, were assessed. Findings revealed a significant association between elevated CDE and increased Hyp/Arg, increased P(A-a) O2, decreased 6MWT, DLCO%pred, and decreased FVC%pred. However, no statistically significant association was found between CDE and FEV1%pred or FEV1/FVC%. The mediating effect of Hyp/Arg was significant for CDE's impact on P(A-a) O2 and DLCO%pred but not on 6MWT and FVC%pred. These results highlight the role of Hyp/Arg in mediating the association between CDE and lung function parameters, shedding light on potential therapeutic avenues for mitigating coal dust-induced lung function impairment.