Calorific value is a key indicator that judge the quality of low calorific value coal. The method of measurement on the low calorific value coal have not been reported. Oxygen bomb combustion method was used to determinate the heat of low calorific value coal. To get more accurate results, the appropriate combustion-supporting material is selected in our experiment. The best combustion addition was explored using the standard addition method making the error of the measurement more smaller. The experimental results show that the coal can burn more fully when adding the Benzoic Acid to it. The best experimental conditions are as follows: coal and combustion are compressed respectively, and the mass ratio is 1 : 1.