A new organic photochromic function material containing pyrazolone-ring, 1-phenyl-3-methyl-4-(4-fluobenzal)-pyrazolone-5 thiosemicarbazone (PM4FBP-TSC) was synthesized and characterized by elemental analysis, IR spectrum and H-1 NMR spectrum. The photochromic properties and photocolored kinetics of PM4FBP-TSC were studied by Time-dependent UV-vis reflective spectra and fluorescent spectra under irradiation of 365nm light. The structure of PM4FBP-TSC was determined by single crystal X-ray diffraction. Space group 3 Pbca with cell dimensions of a = 18.445(4) angstrom, b = 11.987(2) angstrom, c = 19.249(4) angstrom, V = 4256.1(18) angstrom(3), Z= 8 and R = 0.0521. The crystal structure analysis of photocolored product of PM4FBP-TSC showed that the photochromic phenomenon was due to the photoisomerization from enol form to keto form, and the mechanism of intermolecular proton transfer was applied to interpret the photochromism. The photoisomerization belongs to the first-order reaction by computation, and kinetic reaction constant is k(1) = 6.85 x 10(-5) s(-1).