By molecular beam epitaxy technology, reflection-mode (r-mode) and transmission-mode (t-mode) GaAs photocathode samples with identical uniform doping or exponential doping are prepared. Their spectral response are measured based on the on-line spectral response measuring system and via fitting to the experimental curves, the electron diffusion length and integral sensitivity are obtained. These results indicate that, after the cathode module processing of the t-mode sample, the decrease of the electron diffusion length for sample with uniform doping is twice that for sample with exponential doping, the reduction of the integral sensitivity for the latter is smaller by 3% than that for the former. The exponential doping way is beneficial to reducing the influence of cathode module process on photoemission layer of photocathode materials.