In this paper, spectral response characterization of New S25 and LEP photocathodes is studied. Influences of photocathode structure parameter,photoelectron escape depth and photocathode thickness on spectral response characterization are theoretically analysed. Its potentiality for practical trialkali photocathodes is calculated. It shows that to make trialkali photocathodes having the merits of New S25 and LEP photocathodes can compare with the NEA photocathodes on spectral response characterization.