Aiming at the application requirements of monochromatic X-ray source in the field of medical detection, an optimized design scheme of tunable X-ray fluorescence monochromator is proposed. Firstly, the penetration depth of X-ray photons in human skin, bones and fats under different X-ray energy bands were analysised, and the optimal target angle, X-ray generation efficiency and radiation characteristics were calculated by using the Monte Carlo N Particle Transport Code (MCNP), and the metal anode target material was optimized too. On this basis, the single-energy X-ray conversion efficiency of the secondary copper target under different anode voltages (kV) was calculated by establishing the target structure, and the proportion of the Kα characteristic spectrum was also calculated. These relevant works could provide a basis for the optimization and application of the medical X-ray fluorescence monochromator.