X-ray optics and systems have been widely used for applications such as plasma diagnostics, X-ray spectroscopy, astronomical observation and material analysis. The spectral characteristics of the optics and systems need to be accurately measured, for which a high-brightness monochromatic X-ray source is indispensable. Synchrotron radiation facilities provide the most reliable metrology, but their measurement timeliness is limited because of the allocated user beam time and long distances to reach the facilities. Commercial X-ray measurement equipment, such as X-ray fluorescence spectrometers, X-ray reflectometers and diffractometers, are only capable of measurements of small-size optics at a few fixed energy points. Desktop monochromatic X-ray sources that combine X-ray tubes with dispersive optics have provided a laboratory-based approach to calibrating X-ray optics, where the dispersive optics usually refers to multilayers, gratings and crystals. Multilayers are distinguished by their high luminous flux and wide working energy band, but their spectral resolution is relatively low; X-ray gratings allow for much higher spectral resolution, but the fabrication processes are quite difficult for extremely dense grooves for X-ray diffraction. Crystals have a naturally unique dispersion capability in the X-ray band that can substantially improve the spectral resolution. Common-used planar and cylindrical crystals have limited effects to enhance the system throughput because of relatively weak focusing capability in one or both dimensions; complex aspheric bent-crystals, such as toroidal, parabolic and hyperbolic crystals, can reduce aberrations and focus in both meridional and sagittal directions so that system throughput and spectral resolution can be significantly improved. However, aspheric bent-crystals are difficult to fabricate and have many limitations for application; and the aberration would deteriorate abruptly if the incident angle deviates from the designed value. Spherically bent-crystals enable two-dimensional focusing and are relatively easy to be fabricated; therefore, they have been widely used in X-ray spectrometers. Conventional spherical bend-crystal spectrometers adopt the Johann scheme, where the light source and the image plane are located on a Rowland circle with a diameter equaling to the radius of the concave bend-crystal. By applying Johann scheme, better focusing and higher spectral resolution are obtained in the meridional direction, but the brightness of the spectral lines acquired in the image plane is largely decreased due to light divergence in the sagittal direction. Therefore, it is necessary to optimize the optical structure to improve the intensity of dispersed monochromatic X-ray. In this paper, a desktop method for obtaining high-brightness monochromatic X-ray is proposed based on a spherical bent-crystal focusing structure. It achieves monochromaticity in the meridional direction using crystal dispersion, and obtains high brightness in the sagittal direction simultaneously based on spherical-mirror focusing. A geometric model is developed to theoretically compare the efficiency of collecting light of the spherical and cylindrical bent-crystals; also, the dispersion and focusing performance of different optical layouts with spherical and cylindrical bent-crystals are simulated and evaluated. Both theoretical and simulation results show that the spherical bent-crystal focusing structure has an excellent performance in terms of focusing characteristics, with the brightness of the spectral line obviously increased, compared with the cylindrical bent-crystal. In view of the monochromatizing requirements of the Al Kα₁ line, a device based on low-power Al-target X-ray tube is designed and adjusted, and its performance was tested by spectroscopic experiments. Measurement results show that with the X-ray tube working at 7 W power and CCD exposure for 10 minutes, the count of the full-field spectrum of the Al Kα₁ line is greater than 2×10⁵ with a spectral broadening of about 0.592 eV; when introducing a 200 μm beam-limiting slit, the spectral broadening is further reduced to 0.493 eV and the CCD count is about 2×10⁴. The results have verified that the device can effectively obtain the high-brightness Al Kα₁ line, and also provides a new technical approach for accurately measuring the spectral characteristics of X-ray optics and systems.