Abstract: In order to solve the problem that the apparent density measurement result of the coal body is inaccurate due to its small particle size, the feasibility of the coal seam apparent density measurement by simulating coal seam method is researched by theoretical analysis of the relationship between the coal sample particle size and the apparent density. Using the self-developed visual density measuring device, nine coal samples with different metamorphic degrees from different parts of the country were selected for experimental study. The results show that: in a very small range, the apparent density of coal samples increases with the decrease of the particle size of coal samples. When the particle size of coal samples is large enough, the apparent density of coal samples will tend to nearly constant value. With the increase of coal metamorphism, the apparent density of coal increases first and then decreases, which is same to the change rule of coal metamorphism degree and coal micropore volume, porosity and coal adsorption capacity. For each coal sample measured twice under the same moisture content, particle size, molding pressure and surrounding rock pressure, the analysis found that the apparent density measurement error is less than 0.5%; the error difference of the apparent density obtained is no more than 0.33%.