Abstract: In this paper the principle, structure, performance and application of a fluorescent radiation source excited by protons are described. When the K-400 proton accelerator provides a proton beam of 1mA at 270kV, the source intensities at nine energy points between 183eV and 3OOOeV are about 10¹⁰～10¹³ photons/sec. The source has been employed to develop diagnostic techniques for low energy x rays.