The invention discloses an internal standard method based quantifying method for a thermal cracking product of additives for tobacco. The method is characterized in that a sample is pre-cracked by a gas chromatograph, a mass spectrograph and conditions, thermal cracking product is separated to be detected, and the thermal cracking product is retrieved and determined according to retention time and a mass spectrum database; then, an internal standard substance is selected and prepared into the internal standard solution with certain concentration, and the cracking product ingredient to be quantified is prepared into the standard solution with certain concentration; in a cracking tube, the equivalent internal standard solution is respectively added into the sample to be cracked and the standard solutions with different concentrations to carry out cracking and separating detection; the cracking product and the internal standard substance are determined according to the retention time andthe mass spectrum database; and a standard curve is drawn according to the ratio of the cracking product peak area to the internal standard substance peak area so as to quantify the cracking product.The method has the advantages of accurate quantification for thermal cracking product of additives for tobacco, good reproducibility, large information amount, no limit to physical state and the like.