The absorption spectra and excitation spectra at room temperature, the laser-induced fluorescence spectra and the fluorescence lifetime both at room temperature and liquid-nitrogen temperature of a Cr:KTP crystal are measured experimentally. On the basis of the results the ligand parameters, absorption cross-setion, emission cross-setion and quantum efficiency (QE) of the active chromium ions are calculated. It is found that the chromium ions are in the weak ligand, but show strong electron-phonon coupling. The lower QE at room temperature is assigned to a strong nonradiative relaxtion. No spectral character of the chromium ions of tetrahedron is observed.