Because of the particularity of thermal coal, the same index can be expressed by different "bases". "Basis" refers to the state of the coal sample on which the test results are based. Commonly used "bases" in coal quality analysis include air-dried base (represented by ad, that is, air-dried ba-sis), dry base (represented by D, that is, dry base), received base (represented by ar, that is, received base) and dry ash-free base (daf, that is, dry base). If there are two kinds of calorific value of coal: high calorific value and low calorific value, and the results of coal quality analysis have the above four benchmarks, there are eight ways to express calorific value. 1 Calculation of calorific value received at the base surface At present, most of the imported thermal coal trade is priced by calorific value received at the base surface, and the calorific value received at the base surface is calculated by testing moisture, hydrogen content and calorific value after the coal analysis sample reaches the humidity balance with the surrounding environment, that is, the air is dry. The formula is [1]:Qnet, ar=(Qgr, Ad-206had). (100-mt)/(100-%mAd-)-23mt (1) where: Qnet, ar- received low calorific value of coal sample, /gqgr, ad-higher heating value j of air-dried coal sample.