Confocal X-ray fluorescence is a directly non-destructive analysis technique with spatial resolution, widely used in materials, biology, mineral sample analysis, archaeology, evidence traceability and other fields. The confocal X-ray fluorescence spectrometer work is based on a polycapillary X-ray lens. A polycapillary focusing X-ray lens (PFXRL) attached to the X-ray tube is used to focus the divergent X-ray from the X-ray tube to the output focal spot with dozens of micron diameter and high power density gain. A polycapillary parallel X-ray lens (PPXRL) with an input focal spot placed on the front of the silicon drift detector is used to receive the fluorescence signal from the specific region. The overlap region of the output focal spot of the PFXRL and the input focal spot of the PPXRL in the confocal X-ray fluorescence spectrometer is called probe volume. Only the sample in the probe volume can be detected. The spatial information of the sample can be obtained by the relative movement of the probe volume and sample point by point. The size of the probe volume determines the spatial resolution of the confocal X-ray fluorescence spectrometer. Thus, it is significant to measure the size of the probe volume. The shape of the probe volume is similar to an ellipsoid. The size of the probe volume can be expressed as the horizontal resolution X, Y and the depth resolution Z, as showni n Fig.1. The detail size of the probe volume of the confocal X-ray instrument is commonly measured by the metal wire ormetal film using the knife scanning method. To precisely measure the probe volume size, the diameter of the metal wire prefer small than the probe volume size. It is difficult to place the metal wire close to the probe volume because the probe volume size and mental wire diameter are dozens of microns. According to obtain the changing curve of the probe volume size and the energy of the incident X-ray beam, various metal wires were used, which is a waste of time. The metal film is suitable for measuring the depth resolution of the probe volume (Z). However, it is difficult for the metal film to measure the horizontal resolution of the probe volume (X, Y). To solve the problem mentioned above, a special sample of series metal wires stick on paper was used to measure the size of the confocal volume of the confocal X-ray instrument. To adjusting the special sample close to the probe volume, the probe volume can be placed in the plane of the paper. With the assistance of the digital camera, the metal wire can be rapidly placed close to the probe volume. After putting the metal wire close to the probe volume, two-dimensional scanning is performed along with two directions of the probe volume with the help of the motorized translation stage. The changing curve of the probe volume and incident X-ray energy was obtained by processing the data obtained from the two-dimensional scanning. In this study, the probe volume size of the confocal X-ray instrument in our laboratory was measured by the method proposed above.