Abstract: The current function relationship (w_o=1.724×w_TOC) between organic matter and total organic carbon needs a correction because it is not suitable for the new materials. As a significant index of shale gas exploitations, the determination of total organic carbon needs close attention. In this paper, a description of a modified calcination method that has been used to study samples from the south of Ordos Basin is described. X-ray Fluorescence Analysis (XRF) has been applied to determine the compositions of shale in order to reveal the factor controlling the ignition loss of the calcination method. TG-DTA analysis has been used to determine the calcination conditions, which could distinguish mineral salt whether decomposed or not. A linear relationship could be established by fitting the ignition loss value of the calcination method and standard total organic carbon value (TOC) of the CS analyzer method, which could be applied to determine TOC by the conversion relationship between loss on ignition and TOC. Results show that the best calcination temperature is 480℃, and the preferred reaction time is 1.5 h. Two function conversion relationships have been established at the above-mentioned conditions. The relative errors between values from the conversion relationship and from the equipment analysis are 1.691% and 0.486% with detection limits of 0.41% and 1.60%, respectively. The traditional conversion relationship could be corrected to w_o=2.125×w_TOC. The proposed method avoids the ignition loss in traditional calcination method that results in under-representation of organic matters for the decomposition of mineral salt at high temperature, and can precisely measure the organic matters or organic carbon in shale.