The focal spot size and depth of the X-ray source are crucial parameters for X-ray spectroscopy, especially for micro X-ray diffraction and micro X-ray fluorescence. Determining these parameters efficiently and accurately is important for the application and development of the X-ray source. The existing methods for determining these paraments of X-ray source all have their limitations, especially for determining the micro focal spot X-ray source. The tapered glass monocapillary X-ray condenser (TGMXC) is a common X-ray focusing device. According to the filter property and the geometrical characteristics of the TGMXC, the conclusion that the energy upper limit of the focused X-ray of the TGMXC is affected by the focal spot size of the X-ray source can be obtained. The relation between the energy upper limit of the focused X-ray of the TGMXC andthe focal spot size of the X-ray source, and the distance between the TGMXC and the focal spot of the X-ray source was proposed. A method of determining parameters of the X-ray source based on TGMXC was designed. Measuring and determining the parameters of the TGMXC and placed the TGMXC in front of the measured X-ray source to form a focusing X-ray path. In the case that the focusing X-ray path is collimated and ensures that only the single reflected focused X-rays, TGMXC is detected, though changing the distance between the X-ray source and the TGMXC and using the energy spectrum detection system to obtain the corresponding focused X-ray energy spectrums. Though calculating and analyzing the energy spectrums, the maximum energy of each spectrum, namely the energy upper limit, is obtained. The focal spot size and the focal depth can be obtained simultaneously using the above relation and linear fitting. Parameters of a micro focal spot X-ray source with a Mo target were determined by this method. The manufacturer gave the focal spot size and focal depth as about 60 μm and 20 mm and were obtained by this method as 60.1 μm and 19.7 mm, respectively. The conventional pinhole imaging method was also used to determine this X-ray source, and the results were 60.3 μm and 20.1 mm, respectively. Compared with existing methods, this method can determining the micro focal spot X-ray source and has potential practical value and development for determining the high-energy X-ray source.