In coal detection, the overall quality obtained by the quality of coal samples in the sampling unit has two methods : weighting and matching. Different detection items are suitable for different methods. The matching method is mainly applied to crucible expansion sequence, ash melting, Hardgrove grindability index, bond index and colloid layer index 5 experiments. Due to the different particle size and test conditions required by the experiment, the particle size requirements are different when the ratio is different. According to the relevant standards, the particle size of the five experimental ratios is verified. The ratio result of the sample with a particle size of 13 mm is used as the reference value, and the ratio results of the samples with a particle size of 0.2,3 and 6 mm are compared respectively to determine the suitable particle size at different experimental ratios.