When measuring a coating thickness by X-ray fluorescent analysis, the preliminary calibration of the detection system is required using reference samples with a known coating thickness. This operation is quite time-consuming and gives results only for a certain detection system and a pair of elements (the base material and coating). In our study, the calibration curve has been obtained by the Monte Carlo calculation method using the MCC 3D software. In so doing, we calculated the dependences of the ratios of peak intensities of fluorescence lines from Fe Kα (substrate) and Zn Kα (coating), as well as Cu Kα (substrate) and Au Lα (coating) on the values of coating thickness. Moreover, the coating thickness determination errors were obtained. A conclusion was made about the possibility of using the Monte Carlo method to determine the coating thickness without preliminary calibration.