Abstract: A new model which describes the attenuation of X-ray in the X-ray thickness gauge was proposed. Based on measured data of several calibration plates whose thickness is already known, this model was compared with other gauging models mentioned in other papers according to different numbers of data points, different data point distributions and other situations. The calculated values with the new model are in good agreement with experimental data. When the number of data points decreases and the distribution of data points changes, the new model maintains a hign accuracy and presents a better numerical stability than other models.