Abstract: In order to meet the needs of Tongxin Mine for online monitoring of ash of run-of-mine coal underground, a mine passive ash meter is developed and put into service. The ash meter is designed based on the principle that coal ash is directly, correlated with natural radioactivity, and through the use of flameproof γ-ray detector made materials featuring a high radiation transmittance, the optical fiber communication analysis device powered by shielded transformer, and the both internally and externally shielded cost-effective environmental screening structure. Practice shows that the meter works remarkably well; compared with the analytical value, the root-mean-square error of the measured value is smaller than 1.26%; and with the use of the measured data to direct mining operations, the ash of run-of-min coal is seen to be decreased by 0.76 percentage points on an average annual basis. The use of the ash meter has attained the objective of strengthening coal quality control at the source.