Abstract: The three-group diffusion theory model is selected as theoretical treatmentmethod of the in-hopper neutron gauge for measuring the moisture content in thepellet material. The numerical calculations for the pellet material with differentdensity and different chlorinity are carried out. The experimental results arereported. In the moisture region of 4--14wt%, the detector count rate linearlyincreases with the moisture. The influence of the density on measuring moistureis 0.12wt%/1wt%, the influence of the chlorinity is 2wt%/1wt%. For the highlyprecision measurement of the moisture, the correction of the density and thechlorinity must be made. The theoretical results are compared with the experimental results, and theexcellent agreement is found through the efficiency correction.