Abstract: UV-visible rejection ratio is an important parameter for determining SNR of all-day ultraviolet detector system. In order to study the effect of Cs sensitization on UV-visible rejection ratio S280 nm/S320 nm of Cs2Te ultraviolet photocathode during the activation, many activation experiments by using three different groups of Cs content were carried out. Respective comparing the results of UV-visible rejection ratio and the spectral response curves of 200-400 nm, the rejection ratio values of Cs2Te photocathodes activated with different Cs content varied from 4.0 to 7.6. As Cs content grew, the integral sensitivity of photocathodes increased correspondingly between 260 nm and 320 nm, while the growth of the radiation sensitivity at the peak of 256 nm was not remarkable. So this paper focused on the influence of Cs content on the spectral response whose wavelength was more than 320 nm.