The mechanics of electron transport and properties of back-reaction kinetics were investigated by intensity-modulated photocurrent spectroscopy (IMPS) and intensity-modulated photovoltage spectroscopy (IMVS). The theoretical expression fitting the experimental data of five different porous TiO2 films applied in DSC and the values of absorption coefficient (α)，the diffusion coefficient (Dn)，electron lifetime (τn)，the electron transit time (τd) and IPCE can be obtained. The results showed that the electrons transit faster in the thinner films，while the electron concentration increase in the thicker films. The influence of film thickness on the electron generation，transport and recombination processes was investigated in the microscopic level in this paper.