In order to investigate the optical performance of the Wolter-I X-ray mirror shell and to grasp the focusing and testing methods of focusing mirror, the performance of single-layer Wolter-I X-ray focusing mirror was studied. The defocusing, focusing, and off-axis conditions of single-layer focusing lens were experimentally tested in the 100-m vacuum X-ray calibration facility at the Institute of High Energy Physics, Chinese Academy of Sciences. Optical performance parameters such as focal length, focal spot distribution, angular resolution (half energy area is 17″HEW on-axis and 90% energy area is 44″W90 on-axis) were analyzed and calculated. Compared with the data of MPE, the performance parameters are basically the same, and the W90 is better than that of MPE. The experimental results agreed with the simulation results, which provides a basis for further research on image quality. Through experiments, the alignment and testing methods of focusing mirrors are mastered, which will play an important role in the load calibration testing of X-ray astronomical satellites in the future.