The properties of Si-chemical vapor deposited (CVD) diamond interface were investigated by a measuring of CVD diamond films charging under illumination (in a photon energy region from 1.0 to 5.8 eV) as a result of photoexcited electrons and holes injection from silicon substrate and their trapping in a diamond layer. The photocharging was estimated from a change in the dark values of the contact potential difference which was obtained by a dynamic capacitor (Kelvin) method. Three characteristic energy thresholds for electron and hole photoinjection were obtained : 2.8, 3.8, and 5.4 eV. The band model of silicon-diamond interface was proposed on the basis of the experimental data.